The "universal" crossmembers I've seen require welding after fit-up.
My '65 C10 has no crossmember, except a light one for the e-brake. My old 3-speed tranny doesn't even have any holes or boss for mounting. The 4-speed is out of a '74 car...I had to mill off some of the rear mounting to clear the e-brake!
My understanding is that if you use a cast iron bellhousing (as opposed to aluminum) you'll be OK for a manual trans. If you're mounting an automatic, you NEED a rear crossmember.
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