I believe you can get conversion engine mounts from Schumacher or PST.
If you go the v8 k frame, the later spool mount is said to be better than the older biscuit engine mounts. I would look for one that is loaded, including disc brakes. That way you can drop the old one(and sell it)and bolt the v8 one up after any refurbishment/modifications.
Chris at Motech in Temecula now owns Schumacher
and his mounts are extremely nice with great fit!
I have used several of them. He makes exactly what you need.
They are what I used on my 73 Roadrunner Stock Eliminator
that runs 10s and they do the job.