[grumpy]

blykins,
When you're at the meet, check out the RUG model 10 bolts, they're cheap since they are of a later vintage, but are very similar to the HEH 64-66 "collector" big input shaft models.
They were the Type 5 four speed and not as sought after, they were in the 67 thru 1973 FORD/MERCURY/MUSTANG that uses the C1MM mounts just as the original COBRA.
The RUG models were in Galaxies, Fairlanes, Torinos, Cougars, Falcons, and Mustangs. The RUG-AK, RUG-AS, RUG-AU, RUG-AZ, RUG-BA1, RUG-BG, RUG-BG1, and RUG-V1 are all 31 spline that a lot refer to as a NASCAR box, the only NASCAR box in the RUG series are the RUG-AZ1 close ratio and they are the "NASCAR" toploader from this series.
The second gear determines the wide or close ratio model, by having 28 teeth on the "close" and 31 teeth on the "wide" ratio. Any swapper will have the cover loose and let you count the teeth, but his price will let you know. With your 390 FE the wide is as good, if not better for street, depending on your rear gear, I prefer the wide since it does not load the motor and let's you really use first gear.
The small input for the 289/302 and 6 cylinder cars are fine in the 2400 lb cars
You will need a HURST shifter and modify the lever and mounting plate for it. Final result, very few can tell the difference.
Good luck on the "bartering" since there are some that look for big bucks
since its a "toploader". In LA, ARK, TX, OK, these normally will sell for $250.00 in "need of rebuilding", but good gear sets.
grumpy