Well........
I found your dist. # (427965C91) in the MT-132 ('73 up Loadstars) under 392 production #'s ,it is a Holley 1510 w/governor,without tach drive.That pn is not in the MT-127 ('71-73) and as I remember it in '76 the 1530 electronic dist. was the more common dist. used. I won't say "standard" because with IH there was no such thing. So the best estimate is '73-'75.
A 4150G Holley carb. sounds correct,there should be a 3/16th steel line going from the dist. to the gov. on the carb.
I read the threads from BP and I'm the one who posted the links in another thread. They are off on when
Improved cooling was introduced,it was more like 1971 and maybe earlier but without the MT-112 ('62-70 LS) I can't confirm that. I checked the water pipes #'s and they are the same in both the MT-127 ('71-73) & MT-132 books as are the head gasket sets. I know the left bank pipe for pre IC 392's was longer and has more bends since it went to the head and not the block. The reason it was changed was kinda covered in the one BP thread,the heads had cracking issues between cylinders.
I won't go into the rocker arm theory,it was by engine serial number which the MT-127 notes but without giving the sn break.
The 132 only lists them as Boat & Cast types with no sn notes.SO that is an inaccurate way to date an engine.
The letter/year table according to one poster (the OP?) is from a
non IH book on tractors so I can't say if it covers truck engines accurately.
Your block could very well have been cast in '72 but that doesn't mean it was used in production right away either.
12 yrs.exp. in IH dealer parts dept.
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