Hey! you are about to do the same as me!!! I have made a 34 roadster from a collection of bits and it looks very close to the real thing. I am waiting to get photos on disc and I will put them up on a project site. To get scale I went to a show and politely asked an owner if I could use his (unfinished) 34 as a template and he was happy to oblige, I made cardboard templates of what I viewed as critical lines and took about 500 measurements using dressmakers tape. Next I went home and made a seating buck which essentially was the floor pan only made from 20mm plywood and bent tubing to make a skeleton frame, by the way I used an overhead projector and a picture of jamie musselmans 34 to get a side profile and cut two more piecesof ply which ended up as the side reference points for the boot lid and daisy panel as well as the lower boot panel. Not having an english wheel I started to search for a car with the same double crown curve as a 34. I found it in a junkyard and paid $150 for a Toyota Hi Ace 12 Passenger Bus ROOF!!!!! Believe it or not this panel has the same contours as a 34 roadster back you just have to know how to cut it into fitting. If you make a buck like I did you will soon see how the roof fits the curve of the skeleton frame. Bonus number one from the old roof was the support frames could be used to enhance the strength of the body, I used mine to lock the back of the body to my homemade wheel wells. So er gunnulf go for it. Speaking of welds I used a mig and 0.6mm wire and used only the steel from the roof panel as it is aluminium killed from the factory going real slow I minimised the warpage, To make the mould shapes around the bottom of the body I used my home made bead roller across the midddle of the back and made hardwood forms to make the corners. The bead over the wheelwell is made from 16x1 round tubing bent to shape then run over to make it oval this was then welded all the way across the wheelwell (took days) both to the roadster back and then to the wheel well in tiny increments.
As far as the chassis plan goes Wescotts the glass body guys in the US has copies of most Ford chassis dimensions with all the hole positions marked. I made my own but that is another story for my journal. Cheers