...In the picture of the Chevy crate engine it looks like it has a very compact set of "block hugging" style headers. I think that's the best choice. I'd like to put the top rail where is makes most sense and route exhaust around it. People always put curves in headers, but not chassis rails. We'll see. Every day I get up and plan world domination.
...If I had a junk V8 handy and some real life chassis mockup going on I would be more comfortable. I think I need to mock up the pedal assembly and see how small the foot well is when moving the engine back....
Agreed that its better to design the headers to fit the chassis rather than the other way around. The stock LS exhaust manifolds are good starting point and headers take a while to build and can always be added latter.
I was planning to use a "plastic" long block from these folks http://www.payr.com/engines-chevy-smblock.htm
and bolt up a bellhousing and (empty) tranny case to do the final fitting and mount locating. A number of reasons: The blocks are very light (you can man-handle them at table height even if you have a ceiling too low for a cherry picker), have all the external bolt holes accurately placed, are reasonably priced ($375) with an excellant
resale, and allow deferal of the big $$ for the real motor until install time. Should net out way ahead when you figure the cost of back surgery... Anyway, if enough space is reserved for things like feet, bellhousing, motor, tranny, etc. the final fitting can be done in the metal.
That said, a wood mock-up with a plastic motor would be cool, plus it would allow creation of some good vroom-vroom sounds. A lot more fun than making race car noises while sitting on a laptop