What didn't you like about the '73 360? My '72 D200 (3.54 gears and 33" tires) has a mostly-stock 360 and it has plenty of torque although the RPM range is limited, runs out of breath around 4000 RPM. I don't dislike it but then I haven't driven a truck with a 340 or Cummins.
To the OP, I like milder engines in trucks. Compression no more than 9-9.5:1 to be able to run regular gas (since mileage will be terrible no matter what), milder cam to not require a higher-stall converter which will slip and build heat when pulling loads. Better heads won't hurt but will improve performance mostly just at higher revs. With a theoretical top speed of say 75 mph (you said you don't intend to go much over 60), there isn't much need for more than about 300 HP, if that. 300 is a very doable number for a 318 with over 9:1 compression, good heads/intake (Performer RPM...?) and a realistic mild performance cam. I think those 596 heads would work fine.