74 F100 engine swap

I have a 74 F100 supercab with a 2bbl 360 FE that I just can not part with, and would like to upgrade to a more fuel efficient engine package. The most I haul in the truck at one time is a tackle box and a cup of coffee. It is a two wheel drive and I believe the rear gears are 3:50. Any ideas on an easy engine/tranny swap I could make? thanks for any help

Just to follow up. I put a 300 6cyl out of a 78 F150 with a C6 tranny in it. very easy. I had to use the motor mounts from the 78. they bolted right to the frame. I had to shorten the drive shaft 1 1/2". Thats about it. The speedo was off a bit. I put a 21T in it from the 78. close but a little off. I was told that I could get a 23T from mustang unlimited. I have checked in to it yet. The radiator from the 78 did not cool very well. I put one in out of a 92 that was a three core works great.