Tilster,
There is no significant difference in the '75 and '77 HEI. The springs, weights, and advance "cam" ramps may differ from year to year, but overall, '75 to '81 are pretty much the same.
1974 was an odd year for the Pontiac electronic ignitions, and the distributor was more like the early points distributors, but with the guts being of the unitized ignition type.
The '83 "TA" will have a Ch*vy engine in it, and that distributor will not fit in a Pontiac engine.
Good luck,
K.
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K
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