I had a 94 FI460/auto and it towed the 68 bronco on an 18 ft trailer all over the place. One summer I put 28,000 miles on it just towing from the Hammers, to Dakota Territory Challenge, Moab about every other week, Rubicon, Surprise Canyon, CO, Farmington, etc. (best summer of my life)
I don't think you mentioned the tranny, but if it is auto, be sure to run synth lube, put on the transgo shift kit and upgraded springs, and a big aux cooler and you'll be fine. Change it every 30k/year.
The 350/460 combo never came with 4.30 gears (chassis cab only AFAIK), so I would assume 4.10 gears. You can help out with mileage a bit by going to a taller tire like a 285/295/315 that should fit without a lift.
Like someone else said, you will get about the same towing or empty; I was actually commuting to school 150 miles round trip down the canyon in UT with the 460 one year. I found with the tailgate down and keeping the speed/rpms down, you could sometimes get 13 mpg. Typically, it was 225-275 per fill up (8-9) average when towing the '68 Bronco on an 18ft heavy trailer and doing 75+ on the interstate in the mountains, so you should get a bit better here at lower alt and no mountains.
You can tow and pass just about anything except gas stations! Sounds like a bargain to me if it is in decent shape and the AC works.
HTH,
Shannon