KTM,
Street and Performance is the king of late-model engines in early cars! They have almost every part to put almost any modern engine into almost any early model car. They have a nice set of motor mount adapter plates that attach to the LS1 and then you can use standard early model motor mounts. The plates locate the engine so that all original motor and trans mounts bolt right up. They also do a complete line of accessory drives and all the little bits and peices you will need including computer programing and engine wiring harnesses. I am doind a LS engine into a 59 corvette right now, and I have used them for a lot of parts.
Regards, John McGraw