Originally Posted by
canklecat
Yep, I have a similar issue with a couple of nearly identical Shimano long cage RDs -- Exage 500 CX and Deore LX. Same derailleur design, very minor mostly cosmetic differences, almost the same model number. Both are nominally 7-speed and will cover an 8-speed cassette with friction shifters, but not indexed. I've considered using a moto tool to modify the stop inside the body.
not sure what you did differently, but i successfully ran an 8spd shimano cassette with veloce 10spd shifters using a 7spd long cage alivio for several years without any modification.