Dust off your crystal ball and GUESS the horsepower !

Correct. That's how I was talking about. If you could find one still in good shape and was a good runner, you could put a good intake and carburetor and headers with a good hot distributor with a loose curve and there's your 300HP. Problem is now, they are getting older and harder to find lower mileage examples.
If I recall, the Mopar Performance 360 crate engines came in 300 HP and 380. The 300 was supposedly a stock truck engine that was normally rated at 230 as installed in new trucks with catalytic converters and manifolds.