['ol Pinion head]

On the "no number" open frame 10SI alts, years ago, my previous long time auto electric shop owner noted to me there was a large supply of new Delco 10SI open frame front castings that made it to the rebuilder industry in the '70's. Scott, that's what you are seeing in your example with a common 71+ 10SI rear case. I first ran across "no number" stamped 10SI open frame alternators in the yards in the mid 80's. As I had a complete '70 1/2 TransAm useage YZ 400 in the garage with its open frame "903" alt, the open frame design of the first 10SI alternators iintriqued me & like many other items, knew there would be restoration interest in them. About the same time, I bought my first 71 455 HO Pontiac. Meanwhile, out in the yards every week, began pulling open frame '927 & '928 alt cores, as well as the "no number" 10SI alts, still have quite a few of the "no number" 10SI's. '71 Olds also had a few open frame applications. Note by mid May of '71, Delco quit using the open frame front case in 10SI alt production, why Delco stopped using the "open frame" front case, am not sure.

At home in my shop in the alternator boxes, have a 1100800 which is the first Pontiac application internally regulated alt. The "800" is original to a '68 GrandPrix. The "800" while not an open frame design, does have it own specific design fluted rear case. The '69 usage '832's were open frame design 10SI alts & had a new design fluted rear case, also shared with several Corvette application alts. Very tough to find. More 10SI open frame alts were used in '70, the "70 V8 Firebird versions, as well as several Corvette applications. Of note, the high horse application deep groove pulley 37amp "837's used by Chevy in '69 and '70 were all closed frame externally regulated 10DN's (have had 4 of those over the years) very hard to come by.