I am a bit confused. I (just) went to Brewer' website (
Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists ) and found three different repo petal sets. One for '66-67 B-body, one for '68-70 B-body and last for '71-74 B-body/all E-body.
The C-body uses a different set as well as the A-body and also for pickups/fans have their own set.
And, FMJ's also have a different set.
Which petal set of theirs did you get?
The A-body petal set should be the closest setup to FMJ (in theory) – but not done a side by side comparison of them to know how much, if anything, is the same.
Here is a petal set from a '79 F (black) and petal set from a '84 Gran Fury (rust colored).
(Note: F/M body with cast iron brake master cylinder will have a slightly different bolt pattern – but that only matters if you are using manual brakes).
The metal frame is the same on both petal sets, as well as the stop light switch..
Everything else is different – and that includes the petals, the pivot shaft (is longer for the second petal) and the left side bracket. The firewall has two extra holes in it. The factory uses a reinforcement bracket (goes in from engine side of firewall), part # 2950680 (
Firewall Clutch Reinforcement Bracket Fits 71-74 B-Body and E-Body Mopar Cuda | eBay ) for that side bracket.
This is a couple of pictures I collected that shows the master cylinder install (both from an A-body):
Hopefully this helps,
BudW