I assume you have a slight to moderate leak between cyl head and header flange? You check gasket fitment and bolts already? Exactly how bad its it? You prolly will only ruin the exhaust gasket and get some soot on the motor. However, any new engine doesn't need to run at sustained speed for that long. So far I've been on three 25 to 40 mile jaunts with my 235/sedan setup to seat the rings. I've been accelerating in 1st and second and letting the engine slow the car back down, to work the rings. You could prolly drive 20 miles, stop at a gas station and check stuff out, let it take a break then continue another 20-30 miles. Lather, rinse, repeat. Bring some tools, a cell phone and a fire extinguisher with you.
Have you done the cam break in? Have you driven it yet? How does it run?
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