If it's gonna be done with mig I'd still suggest an Ni based filler to give the best results.Other option is no preheat and mig it in short bursts to keep the heat down
I bumped into this video when looking for cast iron repair:
One thing though, if you melt the cast iron it goes glass hard - you won't be filing that off. Braze is best imho for all sorts of reasons.
S.
AIUI he's still associated with Lincoln? http://newsroom.lincolnelectric.com...-motorsports-welding-seminar.htm#.VgM4B25hqCk There's a comically bad vid of one of those seminars on youtube... lots of self ego massaging and BSI know that man. He used to work for Lincoln. He was Lincoln through and through so I wonder why hes left them....curious