As Andy F said, a 70 GTX is not that hard to make. I made a mould for our 70 RR as the bonnet is rusty and with the tunnel ram it is now lift off. Lifting off the steel bonnet is getting old very quickly but life as it often does has thrown a spanner in the schedule.
The big thing with carbon is not so much the strength but the stiffness. The modulus of elasticity of carbon fibre is about 5 times that of glass, particularly when you are looking at unis. My plan is a light carbon cloth on either side of a 19mm nomex core. The bonnet is basically square so a 0/90 laminate works well as the stresses and required stiffness are similar in both directions. The core will give the thickness required for stiffness while keeping the weight. As I have a vacuum pump it is no problem getting both high fibre volume laminates and good core bonding. Around the perimeter and the hole for the carbies there will be some extra lamination. At the bonnet pin locations a G-10 compression tube and local build up will be utilized. For the mould I used polyester as it is cheap, for the part epoxy will be used of course.

Basically, once it is off the car, wax it like crazy and level it. Turns out I should have used some PVA in addition as will be seen later.


Then start lam inating. I put a layer of mat down then I believe 3 layers of 24 oz/yd^2 roving plus mat. Ugly but only planning on one part out of it:



Once it is cured need to put a grid on the backside that is nice and level. This grid does two things. It stiffens the mould and when placed on sawhorses and leveled with shims it ensures the part is not warped. The use of a scribe makes short work of marking the braces.



Perfect fit not required, actually a loose fit is in ways better. Easier to level and the tabbing will not create as much of a hard spot.



Transfer height to forward grid cross piece:

The wedge in former picture sets the level to level and it is sitting on the forward cross piece by that height. Set the scribe to that height and mark the forward cross piece:



Double check level fore and aft and athwarthsips:


Grid tabbed in place:



Wedging mould off of bonnet:



Even with the wax it pulled some of the paint. Poor quality paint job and I should have used PVA on top of the wax but I am sure the paint will come out easily.



Clean up the sharp edges and you are done, with the mould at least.

Or order one from the suppliers mentioned.

I know an excellent composite builder in Bristol, Rhode Island who could do a beautiful bonnet for you. You would need to ship the metal one for him to make a mould.