The roller blocks, both LA and Mag, have taller lifter bores and also threaded bosses in the middle of the valley to bolt the lifter retainer spider to. The taller lifter bores have reliefs on the inside of the pairs of lifters that allow the dogbone pieces to hold the lifters.
I would just look for a 5.9Mag block, they are 10 times as plentiful as the 360 roller blocks.
AFAIK all four roller blocks use the same lifters and retainer hardware. Chrysler was not interested in adding expenses when these engines were built.
Magnums seem to be easier to find. If you can find one early enough, pre 95 I think, many of them had the oil passage to feed LA style heads. The passage was eventually eliminated since magnums oil through the pushrods.
If you are going junkyard hopping look for the roller 360 in church vans as most of the pickups I find are stripped bare already. Probably because it's way easier to pull an engine from a pickup than a snubnose van.