You can tow very heavy loads with a small engine and the right gearing, but you won't be towing very fast.292's were put in trucks with 22,000 lbs gross weights, they pulled ok,but no good for fast road work.Low speed torque is meangless on the highway, ya need a cubic inches, like a V-8 if you need to go fast.
I have two 261 powered trucks, one with a 3 spd OD the other with the 4spd OD Richard and Ftyler mentioned. Both trucks have 3.40 rear gears,in OD,that's like a 2.50 rear end gear.Both will tow a 1200 lbs travel trailer in OD at 70 mph on the highway, and it's no problem at slower speeds for occasional use.Unloaded, the trucks will chug along just fine in OD at 45 mph on level ground.
I think for regular pulling of heavy loads, the 3.73's are good, gotta keep the engine spinning at 2500 plus rpm.The OD is nice when cruising along empty.
A 350 V-8 makes more power than a 292 6 at all rpm's and costs less to find and or rebuild.But if ya like inlines, a 292 will do the job nicely.
