[unruhjonny]

Originally Posted by 392Wrangler

Also this car has the M21 close ratio as is shown on the PHS. But a bulletin on Feb 9th 1970 (Again referring to Rocky’s book says you had to order the 3.73 gears set with that trans, but my PHS does not show Performance axle ratio. It does show safety trak though.
Any thoughts?

I believe that the way it worked is best understood by looking at the options through the lens of a period sales book (of which I have a copy; bought it probably twenty years ago):

#358 4-Speed Close Ratio manual (Safe-T-Track req.)
- 22687 with 37R Axle: $195.36

Later on:

#361 Differential Safe-T-Track (Required with 37R Axle)
- 22387-22487-22687: $42.13

The 'performance axle' option would only show up as a cost option for a Formula w/o option #358, but because your car has option #358, the performance axle was already included.

This is why the close ratio muncie was always (for 1970 & prior) associated with a lower gear set;
Only with the options shuffle for the 1971 model year did the close ratio not always require a lower gear set.

Does that shed some light on to the situation?

You made me do some searching - nice car!!

LINK