I have an engine block I'm having trouble identifying. I believe it is a service replacement block. It currently has a 4.18 bore, extra webbing at the crank end caps, vertical ribs on the outside of the block, a 15/64 drill bit will not fit between the cylinder walls (a 13/64 drill will), and the only numbers/lettering I find are; 'DIF', '352' and '4D18'. (The last are located at the bottom corner next to the oil filter adapter mounting pad.) I had read that another tell tale sign is a 3/8" pipe plug at the lower end of the block indicating it is for a truck's external oil return however, I cannot find such an opening on this block but I'm not sure where to look for it either. Any help is greatly appreciated! Many thanks, Don.

 

with a 4.18 bore it sounds like a 406 or 428.the early 406.s did not come with cross bolt main,the later ones did.most fe blocks came with 352 cast in the block