Dad, your math skills are right on. We expect to get (2) seasons (35-40 shows) without any big cash input. Each winter you need to take apart and inspect but the parts on all these DOHC motors are pretty durable. Some motors may need close attention to timing chains & valve train parts. Others need bottom end scrutiny [bolt torque & bearings].If people really through money at these things & get them up to 375 HP they will not get 2 seasons out of them.
It is all about what we engineers call the "S-N" curve. As stresses go up the life goes down. This is why Top Fuel & Funny Cars get basically new engines every 10 seconds of operation [High stress/low life] & car ferries last 100 years [low stress/long life]. Modern DOHC motors are designed to go 200,000 miles as maintained by a 20 year old college student [infrequent oil changes, cheap gas, mixture of short trips and 85 mph trips home for the weekend].