[Power Surge]

Here's my take on it...

First of all, let me use a very good example I had in my shop recently. It was an ERA with a 427 side oiler, stock stroke crank, out of the box Edel heads, cam VERY similar to yours, MR intake and 750 Holley. This engine was dynoed on an engine dyno by the engine builder and made 430hp. I dynoed the car on my chassis dyno, and it made 387 at the wheels. That almost exactly 10% drivetrain loss through the IRS jag rear. I use 8% for a manual trans with live axle.

Now if your car is only putting 300 at the wheels, something is def wrong, especially with the extra cubic inches. Even with the low timing, you should still have mega torque. There can be lots of causes, but we also don't know key things about the motor. If the CR is low, that'll hurt you. We already know the timing is low. The cam could be not degreed properly. We don't know the air/fuel of the tune. Did you get a/f readings when you dynoed? The one thing that bothers me about the whole situation, is that you say you blew a headgasket at 500 miles. I think that motor has timing issues. And by timing I mean cam timing as well as dist spark timing.

If you got a/f readings while on the dyno, let us know. Post a pic of the graph if you can.