Glen, The proper way to fix manifold is: Clean rust off as good as you can get, DO NOT GRIND A 'V' IN manifold. Pre heat to 450 degrees F. (the whole thing) You can then arc weld with a nickel-iron filler material (ni-rod 55) use either AC or DC rev. The first thing you want to do is go to each end of crack and run a half moon bead across the crack, then run another one overlaying the 1st pass 50 %, then you can start welding crack, all of this must be done while manifold is HOT,(never shut fire off) If you do not have a temperature indicator, stick a match to work piece, when match flares you will be 425 degree F. After welding you can grind weld to make it look nice, If you hace any pinholes at this point, reweld. I would recommend a 3/32 in dia. electrode and run it about 55-60 amps. If you have any questions, call me@ 270-474-0122 CDT