260 motor should bolt in. It is approximately the same size as a 5.0L.
Trans not sure about. Mounting, shifter, driveshaft ?
Wiring needs to be addressed, where to get power, starter motor hook up, etc.
These engines had valves that needed lead in the gas for lubrication, we use no-lead now so what to do here other than add lead.
If you can get these things figured out might be ok.
I know about trusted friends but think hard on this, a 5.0 L is the same basic think except larger in cubic inches.
IMHO... if you want a small V-8 stick to a 5.0l, the same but different, more parts available, more power equipment available, will run today's gas without parts changes, has computer operated EFI, has more stock torque, which is better for a truck.
Luck on your choices.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter