If the Cruiser is priced right, buy it anyway and worry about the details later.
Well, the 3-speed adaptor that Advance Adaptors sells is a different P/N than the 4-speed adaptor. So there must be some difference.
There's nothing wrong with the 283. And it's the older brother of the 327 and 350. It will be a bit easier on fuel and will put out less power (if set up similarly). I have a 350 in mine, and enjoy the extra power. But I do wish I could wring some better mileage out of it.
Are you looking at swapping the engine and transmission/transfer into a 79? Or are you just wanting to put a 79 vintage 4-speed into this 73? If I had a blank slate, I'd go with a 700R4 behind a smallblock.
I'd suggest buying the Cruier, and then getting a Land Cruiser catalog from Advance Adaptors http://www.advanceadapters.com/
to see what your options are. This catalog is well worth the money.
Here's a link to the Landcruiser bellhousing adaptors: