you're dead right in your views about welding cast parts... its
tricky, as noted by one other poster noted due to the manganese and
silicone content. I've done a fair bit of work repairing cast exhaust
manifolds, some with tig, but mostly with a torch. The tig can be made
to do it, but you usually need to have at least 3-5 layers of weld to
get a satisfactory result. exhausts are complicated a lot by the
deposits on the inside of then though, so other casts are not as
difficult. I've had good success with lawn mowers. If you are going
into a shop, call around and see who will do it with gas. its true
that using the flame is harder, but in general i think you'll find that
only a few shops will have anyone who can braze at all, and those you
find will be old school old timers who know their stuff. Just finding
someone like this is a worhtwhile experience. You'll want to keep
their number as they will build up old parts with wear bronze, can
usually operate a lathe and mill and often undercharge for their time.
craftsment are disapearing