Ok so a bit of an update.   I  completely scraped my first mold as I just wasn't satisfied with the look and I went and got a better,  more firm foam from the art shop down the street from me.   Got a block big enough to make 2 mom's for $5!  Well I started another the same way I did the first but I then realized what I was doing wrong.   My main concern is of course it has to look great,  but it has to be completely symmetrical.   I couldn't hope to do this and make an inner scoop out of one piece.   I was able to get the angles equal using the guides on the belt / disc sander as it has a way to angle the table that goes by the disc and a slide groove in there so I can follow through with my whole mold.   Anyways,  I stenciled my main design against some thinner pieces of foam I bought and when I created my inside Mills with a nice scoop and the proper angles,  well it wasn't wide enough to fit just flush with the outer side of the frame.   So I tried to recover this piece all last night and I tried doing this by fitting another stencil of the outside design against what I'd made.   No go.   We'll I was thinking about it today and I'm pretty sure I've solved my problem.   I will build the inner scoop as I did the second time,  but instead of just putting a stencil over it like I had,  I'm going to apply what I tried doing to fix it to create the right dimensions.   I'm going to cut up the stencil so there is a piece that follows the frame,  and the bottom edge,  then where I made the angle going inwards I'll apply that piece between the two and fill in the thin gaps created by angleing,  and then lightly sand it to smooth everything out.   I don't want to jinx myself like I did when I tried painting the header myself...,  but I think I might have finally found a way to make a very sweet looking mold for this bike.   And really the overall side view of it has remained very similar,  and I think it has looked great while I've had my gf hold it for me while I stand back and admire it haha.   I'm expecting tomorrow I'll finally have  a mold to fiberglass!   Very excited!

Sounds like you're on your way, nice work man. If I could throw some unsolicited foam working advice your way it would be this:

Find some blue or pink foam. You guys use it for underfloor insulation in the states. It's hard to find in Australia. It's called XPS (extruded polystyrene) and trade names are Dow, HiLoad, Spyderfoam. It sands really nice, is easy to work with and it dissolves in petrol or thinners.

Make your plug (buck, male mould, whatever) from 2 or more slabs of the foam. Glue the slabs together with 3M77 contact adhesive. If you do this, you will have a perfect center line through the whole block to work with. Makes an excellent reference point and you wont lose it like a line drawn on the outside. The centre line makes it really easy to find the parting plane if you're building a 2 piece mould, too.

Once you have one side shaped nice, its easy to make cardboard templates to get the other side to match. Or eyeball it. Its much easier with that center line there.

If you have a car charger or 12v battery and a length of .020 stainless wire, you can easily make a hot wire cutter to block your plug out to close to the right shape. A soldering iron is handy for roughing out, making hollow sections. But do it outside. The fumes are toxic.

Sand the foam in one direction only. It helps avoid the foam chunking out.

If you're using polyester resin, seal the foam plug with packing tape. Really seal it. otherwise the resin will dissolve the plug into a puddle of goo. I use epoxy.

Sounds like you're on top of things. I just posted this in case theres something you haven't discovered. I use foam a lot, building racing gliders. Good luck buddy. Photos?
regards
s

More angles.

So I think I've finished the mold,  here is it set up against my bike.   Thoughts,  suggestions,  before I start to glass it?

Another.   God I wish we could post more than one pic at a time...

Do you think you'll get any cooling effect from this? Or is it purely aesthetic?

That shape, looks like you'll be able to make a 1 piece female mould from it. That'll make it easier for sure. Are you glassing this foam, then making a female mould from it, or a 1 off using the male mould?