Hello and welcome to the forum!
This Engine Assembly Code you've posted, V0504LLH, ends in an interesting Engine Suffix Code, LLH!
The first part is really pretty much insignificant, V = Flint (engine assembly plant), 0504, date code, May 4, the Engine Suffix Code, LLH tells us the year the vehicle was built, HP the engine was originally built with, displacement and the vehicle it went in.
I have not been able to find any listing for an L series Engine Suffix Code for a Small Block Chevy engine.
I have found Engine Suffix Codes L and LL listed for a a big block Chevy engine, both were used on 427 cid in 1969.
No, I'm not telling you have a 427!
I'm simply saying I haven't been able to find the Engine Suffix Code LLH for a small block Chevy 350.
Chevy regularly reuses these Engine Suffix Codes, often several times, but it seems there is no listing for a L series for small blocks.
In the big picture of things, what does it really matter what the engine started out as!?
You know your 350 is an '87 - '95, so it's a roller cam engine, probably with roller lifters as well.
you know the bore and stroke will be the same 'cause it's a 350, 4.001" bore x 3.48" stroke, any rear main oil seal '87 - '95 will fit, any small block Chevy starter will fit, so getting parts really shouldn't be a problem.
Unless of course you go to Auto Zone or O'Reilly's to get a valve cover gasket, the first thing they'll ask you is, "what year is it?", you'll reply, "it's a '81 Camaro, but the engine is a '87 - '95."
At this point, their eyes will roll back in their head and they will probably start babbling!
They can't put that in the computer!
Anyway, being a little creative at the parts counter you'll be able to get what you need.
Good luck with the engine build for your Camaro!