[FortyNiner]

The F2 trannys were non-syncro, so there wasn't much down shifting to be easily had.

Attempting to use a more modern frame will introduce a variety of issues due to differences in width (the F2 was fairlly narrow), spacing (the F2 was shorter from the cab forward), and flatness (the newer frames have a kickup for the bed not present on the F2).

The other issue is your differntial. Beyond the tranny gearing, the rear gears are not intended to go fast. So in addition to a transmission change, you are likely going to need either new gearing or a rear end swap.

Anything is possible. Money, budget, and available skills are always the keys.