My '64Dog Poly 318 has the bellhousing that wraps around the flywheel. I believe it's very much like yours, may even be the same. It weighs a ton, felt like 70lb to me. On my truck and I suspect on yours too, the transmission hangs out on the end of the bellhousing and doesn't have its own crossmember. I took the transmission off first and then pulled the engine complete with bellhousing. It's a bit tricky because you have to get the mounts up and over the engine mount insulator bolts, and there are two front, two back.
I instead unbolted the rear mounts from the frame.

Assembly: First I bolted on flywheel, then bellhousing. It's much more difficult to access the flywheel with the bellhousing in place. Then I mounted the transmission. That was a bad move. The transmission will not go over the rear huge crossmember, so I had to pull it all out and disconnect the transmission, which I put on the ground.
This time I got the stuff lined up and dropped the engine in, however I couldn't install the rear mounts because top of bellhousing hit the cab trans tunnel. So I picked the engine up a little and moved it forward, then installed the rear mounts onto the bellhousing. This time it went together well. I tightened all the bolts and then installed the transmission.

I am pretty sure that your bellhousing will bolt up to a 318. Everything should fit on a Poly motor, and on the LA motor there's one bolt hole that's in the wrong place at one of the lower corners. This is the bolt that holds the two together right next to a dowel. Many people just leave it out, but because where it was located I decided to have a bolt there. I marked where the matching hole was, drilled and tapped the bellhousing IIRC.

R.