If this is what you're after, go with the 300/6 (4.9) and a T-18 or a T-19. 6500 RPM out of a SBF is doable but is going to cost some money. When my Dad and I were racing GT-350s, a 289 (we couldn't use the 302) that could spin that high was pretty pricey (back in the 80s & early 90s). Most guys that wanted that RPM range got them from Jack Roush and paid $10K. You might be setting yourself up for disappointment.

If the Big Six is not your cup of tea, opt for the 351W. You'll get torque but not necessarily efficiency.

I'm putting an early 80s 302 in my '80 F-150. However, I don't expect the truck to do much hauling/towing nor am I expecting fuel efficiency or gobs of torque. I thought about a Pony Car top-loader but I'm not sure how well it would fit with respect to the shift lever and the seat. You may find yourself fabbing up a crazy shift lever or discovering it won't work. Also, don't forget there are a few different "top-loader" transmissions. I'm pretty sure the one you'd like to use is the same one we ran in the Shelbys. I do not think those will fit with the external shift linkage and the shift mechanism being bolted to the tail shaft housing (which might end up being under the bench seat). That said, I'm not super-familiar with 60s F-100s and you would know better than I. Just my $0.02.