Well really want to have the distributor and exhaust manifolds you plan to run on the engine installed for mock up of the mounts. If your planning to run the stock steering box, the exhaust to steering box clearance is a big issue. Once you set the engine and transmission in the truck with the distributor and exhaust installed you'll see that your motor will want to be toward the passenger side of center a bit. Just leave enough room to remove the distributor cap and valve covers and position the motor as far back as possible.

Joe