With a 318 X 2.45 X .69 I will displace 537 cubic inches of air every revolution of the wheel.

If the truck had a 2.5 4cyl with 3.55 gears and no OD it would displace about 532 cubic inches of air per revoultion of the wheel. Some dakotas were equiped this way and I used to drive one and it was ok.

In first gear it would be a different story.

318 X 2.74 1st gear X 2.45 rear gear = 2134 cubic inches per wheel revolution.

150 X 2.74 ist gear times 3.55 rear gear = 1459 cubic inches per wheel revolution.

I would have a lot more tq to accelerate than the 4cyl but cruise displaceing the same amount of air and coresponding fuel as the 4cyl. I would probably get a custom cam ground for it to boost the tq at very low rpm to further help it cruise better.