With a heavier vehicle it is not horsepower you want but torque. The longer the stroke the more torque the motor makes down low where you need it (that is why when GM built a 5.0 liter motor for economy to push two ton cars and light trucks down the road they chose a 305 instead of the earlier 302. The 302 made tons of horsepower but it has very little torque as it uses the short 283 crankshaft stroke of 3.00 inches combined with the bigger bore of a 327 block (at 4.00 inches). This over square configuration allows the motor to quickly rev to 10,000 RPM where it makes lots of horsepower (the force required to stall the motor at that speed). The 305 has a bore that is smaller than the 283's 3-7/8 inch hole; but uses the longer 3-1/2 inch (3.470" actually) stroke of the 350 engine to generate torque.
Same with the big block. The 4-1/4 inch bore 427 which made more horse power revving to 8,000 RPM with a 3-3/4 inch stroke, but not as much torque as the 4.000" inch stroke 454 using the same bore sized block. Horsepower is great for keeping a car rolling down the road at high speed (which is why NASCAR cars used to paint the horsepower rating on the hoods of their cars back when they really drove production cars (stock cars) around and around the track that you could buy on Monday). In drag racing and on the street you want torque to accelerate a car. A longer stroke car builds more torque, by adding more cubes to an existing bore. The 327 with a 4.00 inch bore yielded to the 350 with another 1/4 inch addition to the 327's stroke. When cars got heavier with time GM introduced the 4-1/8th inch bore 3-3/4 inch long stroke 400 small block which was used in station wagons and pick-up trucks to allow them to keep up with the lighter vehicles in traffic.
Remember it takes only two of your eight cylinders to maintain your speed running down the interstate, but it takes all eight or more cylinders to quickly accelerate the car up to interstate speeds.
The classic American approach to accelerating bigger and heavier cars was to use a bigger displacement motor with a longer stroke with every generation. The V-8 was introduced at a little over 200 cubic inches with the 215 cid Ford flat head in 1932. By the time all of GM's other V-8's went away (there really was a time when you opened the hood of a Pontiac you saw a Pontiac small bore, long stroke engine painted turquoise green, or a gold painted big bore long stroke Olds engine in an Oldsmobile, or my favorite a red painted huge bore short stroke Buick engine under the hood of a Buick Electra 225) they had grown to 500 cubic inches.
The little high revving 283 was popular in it's day stuffed between the fenders of a light 1955 shoe box with a four speed T-10 tranny. But when the 327 came out no body wanted one in their hot rod anymore. In 1968 the 350 was introduced to the masses and Chevy made more of them than any other engine. Four out of five cars you see at a car show will have a 355 under the hood (a 355 is a 350 that has been rebuilt and now has been bored 0.030" oversized with new higher compression pistons). Same thing happened to the BBC 396. When the 427 came outtwop years after the 396 was introduced, you couldn't give one away: and 98% of them were recycled into Toyotas or Datsuns.
Bigger is better. Save the 283. Bag it and tag it and store it away under the bench in the garage in a dry plastic bag to keep moisture out of the motor. Look for an 1969-'74 Estate Wagon on it's way to the crusher and pull the 400 SBC out of it: and rebuild that one if you can. If not rebuild a 350 you buy in the bone yard for about $250 into a 383 (a 0.030" overbored 350 with the SBC 400 3-3/4 inch long stroke crank dropped into the block.