On Tue, 15 Jan 2008 14:44:44 -0800 (PST), Skylark Joe
wrote:

I have a 1966 Buick Skylark that ive been in the process of restoring,
while installing a new Y-Pipe the exhuast mainfold cracked. It cracked
by the bolt hole so now it is a slot not a hole. Evertime i try to put
a bolt in it slips right out the slot. I was talking to my local
automotive machine shop and he says just mig weld the bolt it up with
steel wire! Dosent sound too promising to me. Now the manifolds have
never been removed so i dont want ot remove it and crack the bolts.
Can is be welded on the car safely and with a mig Thank You

Given your constraints, I recommend taking it to someone with TIG. MIG
might work if everything is set just right, but you don't have a
"practice piece". TIG allows use of nickel rod, which is more
compatible with cast iron than steel wire, and it allows the welder
to work with the puddle and adapt in real time while MIG pretty much
just goes according to how the machine is set up.

Another option might be to get a trashed skylark manifold to practice
on before going for the money on yours.

Cast iron varies a lot. I've had some jobs go easy as can be but I
had one old Toyota exhaust manifold that whupped me. Even with
preheating, I'd hear "tics" as a weld cooled and the damned thing
cracked somewhere else near the weld. Weld that crack
successfully...tic. And so on. Another reason to get one to
practice on.