Okay, so I lied.
Figured the real world could wait a bit and seeing as how these saws are pretty easy to teardown/reassemble, I went and put it all back together with the spare 2159 carb.
Saw starts, then climbs in revs like a FUD launching from a carrier deck and then dies- guess I should pull the alloy riser and check out the crank seals..........
I discovered what I wanted to discover- the saw runs, so no need for P&C kits, or anything expensive.
Now I can pull it all down properly, clean it all up a bit and put it back together with new bits where needed and good quality sealant in all the usual places these saws tend to leak or suck air from.
Will have to try and search out a new 372 metal boot clamp as well, this one still has that not so nice plastic clamp- though at this stage it is not broken and appears to be holding well.