1) Easier to work on the front of a 602 than a 603 in a 124

2) 2.5 has first gear start, pretty sure 87 does too.

3) 93 has R134a factory fill. Not sure about 92. Earlier have R12.

4) I don't think there's a difference. 2.5 had leather option, not sure about 87.

2.5 has passenger side airbag standard IIRC, not available in 3.0.

How much service documentation is available for each?

$6500 is a typical price for a good 2.5. I mean if you do your research and are patient you can find them for that price. $3250 is on the low side for a good 87. Seller doesn't know what he/she has if the car is in comparable condition to a 2.5 that's worth $6500.

Sixto
... stay tuned