I Am Having Difficulty Finding A Replacement Engine For My 1995 Lumina 3.1 V6. Could You Tell Me What Other Brands, Models, Years Engines Will Interchange With Mine?

The 3100 and 3400 should bolt up with no problem. With a good bit of work, you could also put the 3.4 DOHC or the 3800 in your car. Though the steps involved in the latter two suggestions makes it a very unattractive swap, both cost and time wise.

Pretty much any late model GM vehicle using the 3100 could be used in your car, as far as I know.

your 95 is a crossover year. IF you have a roller cam engine, 96-99 would be interchangeable. IF you have a flat tappet cam engine, only 94-95 would be directly interchangeable. Like Cadgear said, any vintage 3100 or 3400 would bolt in, but may require modifications to make work.

IF you have a roller cam engine, 96-99 would be interchangeable. IF you have a flat tappet cam engine, only 94-95 would be directly interchangeable.
How would one tell the difference between the two without tearing the engine apart?

Grand Prix, for one, used the 3.1. Where do you live? Hard to believe you can't locate one, popular as they are. If you are in the midwest, I may be able to help you.

How about the standard config (non-DOHC) 3.4, like I had in my '00 Impala? I don't hear anyone talk about those. They are physically identical. A little more uumph, too. Might be a nice upgrade.

regretfully , externally, they look the same. The only way I know to tell them apart is to pull the intake and look to see if the gasket has the push-rod guide plates on it. If so, it's a roller, if not its a flat tappet.