Oh dear - my Dad taught me to drive a truck in our Super Duty tanker. 3500 rpm and nice power in a 2 axle / 32,000lbs truck. 5 spd trans with a close 4th, 2 spd rear axle. Juice brakes. MPG? It burned all the regular gas we put in it.
If a spark ignited engine is built to "diesel duty cycle" standards like those old Super Duty's, high block 427's, Chev V6's, Dodge 413's, IH 404 and 549's, Rolls-Royce Merlins, Pratt&Whitney - wouldn't they "cost the same to fix" because they have some metal in them?