If you're able to position the block in the frame temporarily, use cardboard, duct tape and hot glue to make a template, then duplicate it in steel. That's how we fabricated one-off frame and chassis parts for the round track cars on a routine basis. I've fabricated a lot of brake caliper mounts by holding the caliper in place on the disc with air pressure while I made brackets for them.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!