forever.)
If on the other hand it's a B&S get ready to shell out for new parts
as every engine they make is very parts specific and pricey.

Huh? I've been repairing B&S engines off and on for around 15 years now and
have never run into this problem, I've used parts made in the early 70's on
engines made in the late 80's and vice-versa, never had any problem at all
finding good used or reasonably priced new parts for them, though I haven't
worked on any that were newer than early 90's, they generally don't need
more than basic tuneup parts.