trust me i've searched, and i didn't want to look like a retard, but can you use flat lifters pre-87 on a roller block 87-newer???

and while i'm at it, what does HEI stand for

 

Yes, as long as the cam is intended for flat tappets. And, you'll need longer pushrods, as the roller lifters are taller than flat tappets.

High Energy Ignition.

(This is more of a Tech topic than Engine Swap, so I'll move it over there.)

 

Works just fine. Done it many times myself. The flat tappet lifter looks a little funny sitting WAY down in the lifter bore but it works just fine. Yes, you must use flat-tappet length pushrods (7.80" is stock).

Also, you must use a flat tappet style timing chain and remove the factory roller cam retaining plate from the front of the block.

The Camaro in my sig, below is running a flat tappet in a roller cam block right now.

 

You should check for timing chain to block interference, just above the 3 oil galley plugs when running a double roller in a factory roller block. My $20 special cloyes double roller clearanced the block for me in a previous engine (found out 50k miles later-no harm no foul).