Did a little more searching & found this on another forum (cut & pasted):
I think I would watch out for the M68 Pump-Melling had pressure from the OEM's to "lighten" their pump (weight wise), and the castings became thinner, with a rumored switch to powdered metal gears (not good)-the powdered metal gears don't absorb impacts well, and will shatter if they get too much trash through them-
Melling has realized these problems, and in response to an outcry from the performance market, have come out with an upgraded M68 (called the M68A, or Melling Part# 10687)-basically, the casting is better, the pump housing and cover are CNC'd, the housing is phosphate coated, the Gears are upgraded and not PM-they do cost more (I just bought one for my BBC, and it was about $110.00)-
Plus, comparing my 7 year old Melling M-68 to the new one that cracked, you can see there is definitely less material now around that bolt hole. I would just get the upgraded Melling 10687 but I also came across another forum posting where somebody cracked the exact same flange I did.