they hauled huge loads with a 235, the truth is they didn't go very fast that way. And going up hills was slow going
X2

There is nothing (short of a blower) that you can do to a 261 that will produce the same power as a stock 350. Kitchen sink: perhaps 250 hp.

There are no "torquemonsters". The boat load of torque is between 1 and 1.25 ft./lbs. per inch - the same as anything else. It's just at lower and more useful RPM.
A 300 hp 292 will tow the skin off a chocolate pudding at 3,000 RPM, but not much else since the extra power is 2,000 above where you want it, and the 3,000 RPM power is less than stock.
This is the exact opposite of what you want - an engine that needs to be spun off the dial to pull a trailer.
If you want an older L6 get a 302.
If you just want an L6 get a 4200.
I've done some light towing (1 ton Powerwagon, 318 4-speed + car carrier) and 230 hp was never enough.