I found a nice longblock, and wondering how good these things are since i've only used 010 casting 2pc rear main blocks.

Its 10.5:1 comp all forged 383, with afr heads.

i built the vortec headed/HOT cammed 355 in my Nova using an 87 Caprice roller block.. with the parts i used, it had a "magazine HP rating" of around 400hp, with maybe 375HP being realistic. my machinist said he's seen them up past 500hp without any problems.

Its the base of a zz4 crate motor,, and I ABUSED the hell out of one for 4 years,, and at tear down for a MORE POWER rebuild,,,,,,,,,, all was well..

Not all the one-piece rear main blocks came with roller cams/lifters; which means nothing EXCEPT that at least some of them got goofy lifter bore machining; and so you can drop OEM-style hydraulic roller lifters into them--but you get an internal oil leak and low oil pressure.

CHECK THE LIFTER BORES before you fire the engine.

You have to be very carefull with these blocks. Some of the truck blocks that came with non roller cams will NOT work with a roller. You need to look at the lifter bores. If the lifter bore is the same size all the way from bottom to top, then it will work with the roller. If there is a "counterbored" area at the top that is larger than the rest of the bore, then you cannot use a stock type hydraulic roller lifter. I found this out the hard way a while back when I built an engine for my 85 Blazer. It had very low oil pressure and it took forever for me to figure out that the oil hole of the roller lifters was coming up into the counterbored area of the bore and bleeding oil pressure. I dont know why GM did this on some of the early blcoks but they did. So beware !

You'll also want to confirm that the block has a functional fuel pump boss if you aren't planning to run an electric fuel pump.