Classy, Your roof idea has been done so many times before. Not that difficult to pull off.
Your V8 engine choice is okay and it will fit in the Goblin frame. Just as the V6 SC's. The frame (cradle) mods will not be that difficult to pull off. The V8 would give you more forward (near cockpit) weight and a lower center of gravity. The LS4 will bolt to the F40 transmission (60 degree pattern) The only thing is the starter will have to be adapted, since it bolts to the bell housing over the transmission and not to the engine side. This has already been done and there are solutions for it. I would do a AFM delete so it would run V8 all the time.
The LS4 came in the 2005 - 2009 Chevy Impala, Pontiac GXP and a Buick model. There is a GXP engine near me that is going for 910$ (has a punctured oil pan from the wreck). I believe there is one in a Dallas or Houston area salvage yard for less than 1,500$. I can send you the listing site if you want. I believe Stalker had a roller listed for sale for 19,500$
The Stalker XL is almost a Corvette in wheel base and track. Come see me and I'll take you to one being built so you can have a look. Your about 11 hours drive away. I think JBINTX said he was auto crossing soon, and I might come watch him. I could be persuaded to bring my classic Stalker along for you to see in person.
The library should have a book titled How to build a car for 250Pounds (English -- Locost style frame. The McSorley option was a larger frame) It gives you the dimensions of all the tubing and where it goes. You purchase the tubing, cut it weld it. There is a Locost website of builder/owners that website that has all kinds of pictures of traditional builds and a whole section on mid-engine builds. Lonny mentioned Midlana -- he wrote a book about his build.
The Goblin is a fantastically designed chassis. Good on the Design team!! It is simple, bolt together from one donor build. Other kits are built well, but some you have to find parts that fit from multiple donors. My Birkin seven kit is from South Africa. It has Ford, Honda, VW, Toyota and English Ford parts. The Stalker is mostly a GM donor build. Exocet Miata based if you stay that way.
Any thing else I can help you Goblin builders with let me know.
At least you've ridden in a Goblin. I'll do that one day!!
Anyone wanting to try a Saturn Vue steering unit with the controller out? I have one in my shed. (by the way the controller only works with the metal box unit - for some reason it doesn't with the black plastic unit, so just infor)
Dale