The later 6 bolt was a cost reduction. I don't know of any operational difference. I have bolted 8 hole pumps into 6 hole cases, after running a tap into 2 holes. Haven't tried drilling a 6 hole pump. Bruce Roe
Operationally-- nothing.. just two less mounting bolts, one of the many cost saving things that was done in the 70's to the TH 400. The 8 bolt cases are sought after, as they are required to mount an SFI ultra bell. Some early 70's cases still have the material in the pump flange to drill and tap the holes, but that was also removed later in the 70's. So Mike, if your building a serious 400 to go behind your Tomahawk, with an ultra bell, then you need to find either a 6 bolt case you can drill and tap, or an 8 bolt case. JW
