The Frame rails are wider apart (4”, I think) on the ‘73’s, than FMJ bodies. They may still fit just fine.
If not, I know a person who can “re-bend” the bars to fit.
The hardware, especially the differential brackets, are the main item to grab (which should be the same with or without Iso-mounts).
A lot of the “performance” ‘73’s didn’t use the Iso-mounts (but some did).
I went back and looked and the parts do make a difference (with Iso- or without).
FMJ
The frame bracket parts are the same (B vs. FMJ). The sway bar itself is different between both versions (B vs. FMJ) – for one is frame mounted (newer style) and the other is differential mounted (older style). They will both work – pending if the B-body bar is not too wide.
Note: cars that use a rear sway bar will also have a larger front sway bar than a non rear sway bar car will have.
BudW