Length of the old vs new caps works both ways. Sometimes you see a large old cap with the leads bent back under because it's going to two closely spaced terminals. The new smaller cap would fit better.
Lengthening new cap leads with tinned wire is fine: an easy way is to form a "squib" from one of the wires, a tight little coil of several turns that fits around the other wire, and then is soldered. Forms a good connection. When restuffing the squib can hide inside the outer shell and no one will know...
