A hopefully short enough guide on what to do with that nose of your vintage board.

First, why is that long nose there and does it matter? Board designers, aided by better fins and sails in the early 90s, literally flipped the shape of boards around to put the fat part in the back - where the rider is planing - and the thin, skinny part up front. These were dubbed "no-noses" even though the remaining nose was long and thin. These boards were still 265-295cm long (80-130l) like the previous generation. The noses persisted because there was a fear that a shorter nose would spear/pearl/submarine into the back of chop or into a wave on a hard turn. (Spoiler alert: it's almost a non factor) And, in no small part to the feeling that I had the first time I rode a 240cm board of discomfort at seeing so little board in front of the mast.
Another factor for the long nose was that most boards were 55-59cm wide and needed a long, straight rocker line to plane up. The rocker didn't turn up until well forward of the mast track.

In the late 90s, boards started to get wider, so the long rocker could be shortened. As well, that long nose had two very nasty side effects: 1) the upturned nose which in some cases with wave boards was well turned up (think elf shoes) loved to punch holes in the foot of a sail. It didn't take a catapult; simply having the sail fly from your hands in a botched waterstart was sufficient. 2) That long nose was a catapult target. A newbie could and would (I witnessed it), destroy the nose of a Bic Techno 283/293 in a single afternoon.

So, over time, along with noticing that these new 235/240cm boards fit very nicely into the back of an SUV or minivan without a rack or trailer and tiring of making almost weekly nose repairs, people wondered if lopping of the nose of their old board would make sense? Short answer: yes. There are some considerations, however. It's not as simply as taking a hacksaw and cutting your 275 cm board to 235. I mean, you can do that but you end up with some weird side effects.

So, here's some considerations:
1) When we first started doing this, being accustomed to 30 yrs of boards with nice rounded shapes, we struggled with the aesthetics. To make a long graceful outline in the new nose requires shaping the rail a considerable distance from the nose which makes the whole affair more involved. Then new boards came out with pretty much squared off noses from the Mistral Explosion around 2008 to the Fanatic Blast and Stubby currently. Foil race boards in some cases just look like a sheet of plywood (Patrik) so any feeling that your board needs to have that pointy surfboard shape can go out the window. If you still insist, a moderate 7-10 degree angle with rounded corners suffices nicely (use the Blast as a template).
2) You still have to consider the rocker line of your old board. If you go too far back, you end up into the flatter part of the rocker line. If so, you need to be prepared to some significant modifications to the bottom ie cutting some of it off and reshaping the bottom. This gets into an entire different kettle of fish.
3) Similarly, some of those old boards' noses got thick pretty quickly. Even if you aren't reshaping the bottom, you may have to cut back 4-8 inches from the nose to thin it out and keep the rocker line consistent. Here's a version where the core of the board was removed instead of the bottom: https://www.peterman.dk/windsurf-DIY-refurbishing-old-wave-board-1200.htm
4) A couple of construction tips: It's easier to cut back an extra 5cm, glue on fresh foam and reshape that instead of trying to grind away at the skin and foam in an effort to shape things. Most boards have a hard edge from the bottom to rail transition even through the nose. Don't just make your new nose round, shape that little edge. It keeps spray from wrapping around the bottom of the board and up on you. It matters in the winter.
5) Methods: When you start hacking away at an old board, you'll notice how crap the construction really is. "Carbon" means a few threads (literally) running down the skin. In most cases, three layers of glass over foam is sufficient. You don't need the stiffness of a sandwich there and good pvc foam (divinycell, etc) is expensive. If you insist on doing a sandwich, you can use 1/8" cork. If you are worried about nose damage (remember, it's not that much of a target anymore), use S-glass instead of the standard E-glass. It's actually stronger than cf and much cheaper. CF has the advantage in stiffness but not strength (which is why your freeride board is fine in S glass instead of more expensive cf).

Shape your foam, layer up the glass layers with good epoxy (System Three or West), do a poor man's vaccum bag by cling wrap and/or masking tape. Fill imperfections with epoxy/glass microcells (Q-cells) bog, sand and paint with rattle can. If you are doing a bigger job, do the bottom first, then the top. The quaility of your foam shaping and smoothness is key. You can fill/reshape problem areas with bog before you glass. Masking tape is your friend, get lots of it. Mask areas around it so you don't make a mess.

Old boards are cheap. If you make a mess, either redo it or try again. The best part of this is that you'll gain the experience and confidence to make really good repairs on your newer boards. Instead of just gobbing on the 5 min crap in a shoddy repair, you'll be able to do a proper, strong repair on that expensive board.

Some pics from the recent project - this isn't every step and, because of the thinness of the existing nose, I didn't need to do much work on the bottom. Original, cut off nose, nose with new foam glued on, foam and existing sandwich sanded and tapered, new cork sandwich faired into existing deck (layer of glass underneath), cling wrap covering top layers of glass. Finished board:

Edit: added a pic