So long story short, was told this guy has a TA/AAR block and turns out to be a 1979 dated Mopar Performance over the counter block and has been sitting in his shop since the early 1980’s. Now I know a little something about the ‘R’ blocks produced later on, but nothing on the ‘X’ ones. It looks to have a standard bore set of 340 pistons, but the guy will double check the bores when he gets back home tomorrow. The 4-bolt mains look super beefy and dang, it felt heavy like a 440 block.

So my question is:
Are these desirable?
How much hp/tq are they good for?
Is there a value to owning one or just sell it?
Thanks in advance.

More pics. Also, got this 360 from the shop and it has adjustable rockers for some reason. Not sure what it is?

Ultra desirable
Come 2 or 4 bolt
Come 3.91 bore, have seen them check good for use at 4.125 bore. But each one can be a bit different. So, to get to a standard 4.04 340 bore, need lots of metal removed and sonic checking, imo, is a must
Beefier bottom end, filled pan rail, etc
Standard 340 type top end, so unlike 59 degree r3 blocks, roller lifters drop right in.
They can take a lot of punishment. They are my favorite LA 59 degree block
I Ran one at 4.100 700 horse years ago, that block is still in use
Virgin block like you have is worth 3k + all day

The 360 has 273 style rockers on it. Nothing uncommon there, as they were an alternative to buying roller rockers. Check that it has a solid tappet, rather than a preloaded hydraulic lifter.

The main selling point for the X block is that most roller lifters are a total drop in. Otherwise they're very similar to the early R blocks that came much later. Both blocks were machined with factory type tooling, just the casting had a lot more material where it matter.

You shouldn't have any trouble selling the X block, they're defintely sought after by the 59* crowd.

That casting number was on standard 318 blocks back in that era too. Just not the “X” on the front along with the other cool features.

So I talked to the previous owner and was told it was bored out to standard 340 piston size and looks to may be a non-ran engine and just sat in the garage since 1981-1982. The block has 340 mains and he has a time to clean it up when I need something for it.

Will post more info Tuesday. By chance, how would someone build up a block like this? High compression? Turbo? Blower? Nitrus?

They're an early race block, they're not siamese bore, so they're not going to handle a bunch of boost or a bunch of nitrous. Having the extra meat around the crankshaft will certainly help.
The builds I have seen have usually been W5 or Indy headed strokers that make around 700hp

Went to get the block today and my back was not up to the chore of moving it and my garage space got loaded up from the weekend, so I have to make room for it. Will bring it home in a week or two when I’m able to accommodate it.

Useless junk. Contact me, and I'll do you a solid and take it off your hands for a fair price. I need a boat anchor.