Kim,
I was able to work from that same blueprint and in fact I gave it to him to post at his site some years ago. I was able to build these from some scrap aluminum for the big brace and some flat steel plate using just a drill press, angle grinder, some files, and a little bit of arm strength. I uses 3 layers of 1/8" aluminum plate rather than 1/4" steel plate for the big hinge piece. Bonded together with JG Weld and 5 years+ later it still works fine.
I did have some rust inside the front behind the grill. I added some aluminum 1" angle iron and pop rivited in place, this was in the pre welder days. I cleaned everything up, ground out rust, and used the aluminum channel to reinforce things. There really is a lot of meat up there to work with and the bonnet really is quite strong.
Cracks over the wheel arches. Frank used to use some 1/4" stainless rebar. Now I've never seen rebar that small but maybe someone on the list can help. Rebar goes into the arch under the lip and reinforces everything. Weld in place and much, much stronger.
Latches come from the McMaster Carr catalog. Sears under Stainless Steel Adjustable Draw Latches. IThey are pretty inexpensive and rated for 400 lbs. I tried several sets of those nice latches from Winners Circle and after breaking 4 of them went to these from McMaster Carr. Two small self tapping screws to mount and away you go. You need to be able to do adjustments to the latches as the bonnet will take on a slightly different shape after it gets mounted and latches down. SPitfire latches really look cool but a PITA to mount and fit. Frank used them on his Sprite with the fiberglass Speedwell Bonnet but big difference repairing fiberglass than metal.
Need pics, let me know and I can send.