If your truck has a RTO-14613 (a 13spd overdrive, real common) and 4.11 rears, it would go just a little over 70MPH at 2100 RPM. A 3.73 would be a little faster. If you had a RT-14613 (no over drive) it would need a higher speed (lower number) ratio to get up to 70MPH.
You have a good looking truck. What year is it? I see you have 6 spoke wheels on the front, that usually means a 16, 18, or 20K front axle. Usually the older trucks had wege brakes on the front. The shoes aren't a problem, the hardware kits are spendy. I did brakes on the front of my 90 LT9000 last year. The 95 in my pics has S cam brakes, they are easier to work with and more common.
Good luck with your truck!
Is it easy to get Ford related parts for those trucks? I had a LTL9000 and sold it because it was hard to get the Ford related parts like switches and body parts. Ford L series trucks do not seem to be that popular out here even though I liked my truck.