To help out, body “H and N” are F-bodies and “F and G” are M-bodies
On both, there is a 2-door length and a 4-door/station wagon length (roughly about four inch difference).
The A727 propeller shaft is shorter than any other transmission type Chrysler used in either M or F-body (and A904, A833 and A230 used the same, longer shaft), which is about four inch difference.
The 7¼” differential uses a longer propeller shaft than the 8¼” differential does, which is about 1½ inch difference.
The “45's” are station wagons. All station wagons were meant to come with 8¼” differentials (not all came that way due to supply issues, but they were “meant” to).
According to this chart (below), a 1979 HNFG 45 (station wagon or 4-door) with A727 (and 8¼“) should be 48.60 inch from center of U-joint to center of U-joint.
All factory propeller shafts for that year (or any FMJ) will be using 7260 U-joints.
If you are having a propeller shaft made for this car, this would be a perfect time to upgrade to 7290 (or stronger) U-joints which might be advisable if car is going to make any (more than stock) power.
BudW