Surprisingly I have found my Monty Carlo LS with the original 4.3 the easier to find parts for. At least GM used that 4.3 in everything for a long time. The other project I have is an 1941 Chevy. Should see the look on the parts store employee when you tell them it will not be in the computer and then they look and find out it is not in the computer.
On the few occasions I go to the corporate parts stores I tend to give the parts store monkeys crap because I can.
My 1977 truck isn't in their computers for what it is. It's trim level is bonanza. Not custom deluxe/scottsdale/silverado/etc... bonanza. Sure, it's a trim/value package, but no more so than a silverado was.
So when they insist on typing in all different info they go through the year, make, model... then stall.... I don't see bonanza, do you mean silverado? I say nope, go outside, look at the fender and the dashboard. They walk out all brisk, sure they'll prove me wrong. I lean back on the counter and wait. Watch. See them look at fender, through window, and back again. After a few times they return, much more slowly, and dejected.
Depending how much attitude they gave me first I sometimes needle them and ask what it said, and other times I just wait for them to say something to me. But it always turns to "so, what was the part number you said you wanted?"
Unfortunately, areas I've lived lately don't have mom and pop stores where those conversations didn't happen. So, I tend to shop online when possible, or deal with the monkeys when I don't have time to.