here is an ls swap kit for the firebird chassis. anything look familiar? seems like a swap kit like this should solve the engine mount problem as long as it doesn't place the engine too far forward or back. you need space for a fan and clearance for the heads on the firewall. or notch the firewall i guess. anyway, just curious what your engine mount kit looks like in comparison.
http://www.brphotrods.com/products/2...cts/index.html