Regardless of the engine you will need to replace the 4.11 gear set to have a vehicle that will operate comfortably at reasonable highway speeds. By reasonable I mean in the 55 to 65 mph range.

The engine rpm is determined by the tire diameter and the rear axle ratio assuming top gear is a direct 1 to 1 ratio (no overdrive).

Unless you do a full suspension, steering, wheel/tire, and brakes upgrade you will have a difficult to control vehicle at higher speeds.

While I agree that the full pressure 235 or a 261 would be an engine upgrade, perhaps you should consider first putting time and money into swapping in a 3.55 gear set. That change will reduce engine speed by about 15% for any given road speed. Then you can better determine if you need the extra torque from the larger engine to offset the acceleration loss due to the lower gear ratio.

Rusty