Even an easier rule. Limit the tire width to make the power unnecessary.

my first thought also.
The only good rule is no rule. As long as I can remember midgets have been expensive to run, not likely to change anytime soon.
Not to ruffle midget owners or lovers feathers but to me the cost of running one seems crazy when you can have a full size race car and spend less.
As for sealing up engines and such after your dyno run that's crap. What happens if I need to make pill or jet changes to keep my engine from burning up ?
You either need a completely sealed engines (crate) or completely open engine rule.

Did it at IRP / ORP in Clermomt for the 305 cars and trucks. On random nights the Top-5 loaded up and an official rode with the car over to Cozzolino's, about 20 min from the track. They ran each car on his chassis dyno. Over, you're out, under you're good. Pete said it worked and nobody bitched.

Tire and suspension improvements over the years has allowed more HP to the track. Late models learned this year's ago and went with a narrow tire to limit engine costs.
Sprints On Dirt have tried a similar thing this year.

Dynoing engines will become a pain. The easiest most cost effective immediate solution is to narrow and harden both rear tires