So the front mount plate mounts where on the block? Between the bell and block? Or the front of the block? And where would you guys suggest I tie the plate into? The main roll hoop + the middle section of the chassis floor?
The front plate goes between the block and the waterpump, the mid-plate between the block and the bellhousing. See pics below. The first pic shows both front and mid plates mounted to a tubular (front engine) chassis without the engine in place. The second one shows a front plate fixed to an LS engine without the water pump mounted. They should give you some idea of how it all goes together.
One approach to fitting engine plates to your chassis would be to bolt up the block and transaxle, including the front and mid plates, locate this in the chassis where you want it relative to your rear axle line. Then position and weld steel tabs to the chassis, drill the plates/tabs and bolt the driveline in place. You might also consider adding verticle tubes to the chassis engine bay for greater strength and attaching the tabs (or flanges) to these instead. You could also triangulate these verticles along the sides for added chassis stiffness.