i'm sure the block woud be able to take it since it's the same block as a 22R only with smaller bores, BUT...
...you'd have to get forged dished pistons and a bunch of other bottom and top end stuff to increase strength and lower compression, after all that you probably would have spent your money better on a 22RTE
a 22R is pretty much a drop in replacement for a 20R. do you have any stuff that would increase your performance on your truck right now, like a weber carb or header or cam? those things help a lot, a weber can add quite a few ponies by itself
i know DOA racing sells a 20R EFI(essentially a 20RE), never seen a setup like that anywhere. personally i'd just get a 22R shortblock and rocker assembly(the assembly is aluminum instead of steel like a 20R), bolt on your 20R head, a performance cam, header and a weber 32/36(don't think the 38 is legal in california). i'm gonna run this setup when i get some cash, and i have a spare engine with a rod through the block that i can pull the head off of so i can drive my truck until the engine is built up