The 2004R in 1990 would definitely be a multi-bolt pattern trans. That means if you feel back there where it bolts to the engine you will find bolt holes and flange extensions sticking out into nowhere where it bolts to the engine. The 700r4 is a Chevy only bolt pattern so it will match the back of the block perfectly. No unused bolt holes.
I doubt you have a 2004R in a caprice. The only 2004Rs in 1990 to my knowledge were used in the B-body wagons and they were behind the 307 Olds engine with a computer controlled quadrajet carb. 90 was the last year for them, then they were discontinued. Every 305/350 Chevy in a B-body non-wagon car that I have seen had the 700r4. Only the Olds engines got the 2004r.
Hope this helps.