Most cast iron exhaust manifolds don't weld well when old, carbonised and cracked. Don't bother, just find another.
Years ago I had a cracked exhaust one on my 265 Hemi Chrysler, I
was going to weld it. Until I undid it and it fell off in 4 pieces. Was bent from the heat too.
On the other hand, Gafmo broke a bottom flange off his Alfa twinspark's front header a year or more ago. So I MIG welded it back on with 316L S/S wire, and it's still attached...

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
