The tall deck 2.5L pre-dated the later (89+) 'common block' engines. It used proprietary length rods, the same pistons as a 2.2L (I think) and did not have floating wrist pins, and stock would have had an N/A compression ratio (9:1 I think).
The 89+ 2.5L engine uses the same rods, but a different crank and pistons. The pistons have the wristpin positioned higher, and the crank has greater throw - as well as a relief at the bottom of the bore to clear the rods with the larger crank throw. The 89+ is often considered stronger. The 2.5L shipped with balance shafts, which are often removed or rendered inoperable for a few HP and less mechanical complication.
If you have forged slugs and studs in that 2.5L, and dished pistons (turbo pistons, with the lower compression ratio) then you've got a great starting point. Toss a swirl head on there (ported, preferably) and enjoy the increased torque and faster spool of the 2.5L.
The only down-side to the 2.5L is that because it's bigger, it demands more flow - our 8v heads are anemic to begin with - and the 2.5L only makes the head an even bigger choke point, and move max power lower in the rpm range. With a very good flowing head, the 2.5 should have some substantial potential (it's still a driveability upgrade over a 2.2 in a heavy car).