Craigslist 4 Speed - Something doesn't jive?

Yea.

You most likely will need one of these adapter rings:

Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists

Or

Adapter Rings | Passon Performance | Get your SHIFT together!

That trans you bought was only behind small block abodies. It has the smaller 4.35 OD bearing retainer diameter that mate with the hole at the back of the scatter shield/bellhousing.

Did you buy that eBay scatter sheild? Did the seller tell you what the trans side hole diameter was?
I already bought the scatter shield. There seems to be only 1 big block scatter shield available, which is the lakewood/quick time (both are made by Holley from what I can tell). I didn't get the diameter of the bearing retainer, but once I get it I can measure and buy the necessary adapter.

Edit: Holley website has the trans diameter listed as 5.6 in.