I would box the original frame and order some aftermarkett motor mounts{ones that are designed to weld in} ,hang the engine over the cradle and install accordingly,only tack welding the new mounts in.
I Think that those engine bays are pretty deep ,soo a couple of inches higher mounting should not be a problem,but as always ,make shure the clearances are set before final welding.
One of the other members will know more about how to do the actuall boxing than I do .There are some pretty good posts on boxing a frame already on this site,good luck!!!