J have a block that Id,s as a 39 merc or ford tk 39 to 42 have had jn storage eor over 40 yrs accoeding to van pelts web site the center water holes are trapizodial it also has core plugs on the pan rails call me at 541 963 5350
Ihave done 3 of these disc front drum rear the m/c should work ok but have had better luck with adodge pickup worked better 1in bore . You won,t be happy with out power asst. get a8in dbl dia.