Ive found this picture of the car after it was sold to Kay Petre in the late thirties that shows the shape of the Riley chassis from above.. lots of curves!

Really interesting to read because you’re clearly so comfortable working with wood.  Any chance you’d post a sketch of your chassis design?

The plan is evolving and refining on a daily basis but this is fairly up to date-
Box section rails, box section tub made of triangles, hopefully ill be able to get most it from 2 sheets of 8x4. Most of it still needs finessing.

I got some time today at lunch to cut out the last two chassis rail laminates and to cut one of the two 8x2 boards down into smaller pieces for making the floor and seat parts of the tub. I have one 8x2 left which will get cut in half to do the sides (maybe tomorrow? I’ve got Friday and Monday off) which will leave a couple of square feet at most left over in offcuts. I may have to invest in another half sheet of plywood in order to get the rest of the tub done. Tomorrow I’ll have to also assemble some sort of jury rigged router table to trim all the rough cut bits I’ve produced so far to exact size and shape. I’ve a couple of old bass speaker cabinets at home that should work quite well for improvising the router table out of. Thinking about it, they may well be a suitable source of reasonably sized, free Baltic Birch ply..hmmmmmm....

Annoyed cat, radiator grille;

If this car goes horribly wrong and gets scrapped ill save that bit and turn it into a guitar amp.. i made the amplifier section for one for Jeff Beck many years ago that had a Daimler hearse grille/surround over a 15” speaker, and two tone leather over the rest of the cabinet. It was a 3 way collaboration between a guitar maker(cabinet and concept), an amp maker (me) and a silversmith (radiator badge and rille badge were solid silver), it looked super cool.

Wow !    Got some really talented people on here   

The prototype seat bottom support roughly held in place between the 2 of the rail laminates; theres 2 triangles of pine and some more plywood to box that bit up that you cant see, all currently just screwed together. Ill make some proper triangles out of real wood when i can confirm it all fits.
There will then be a load of glue and loads more screws attached.
Ive had an idea regards driver comfort, so the bit of the seat you can see here is basically just the support. The actual seat will be woven Shaker style using 25mm nylon webbing and suspended just above this bit from four 1” wooden rails, connected at the corners. We had a baby this year during lockdown 1.0 and i made mrs Synthpunk a shaker style rocking chair for feedin the minime and drying socks on. the tape woven seat is very strong, comfortable, and springy, which is wot gave me the idea..