Clamp a pair of vise grips on the flywheel ring gear on both sides of the bottom opening in the bellhousing. It's a lot simpler than trying to find the exact TDC spot where air pressure won't turn the crankshaft. With the engine in the vehicle, just put the transmission in gear and chock the wheels or set the parking brake, or both. The test will work just as well with the piston at bottom dead center with both valves closed as it will at the top, BTW, so you could just loosen up the valve adjustments and do it that way.

With compression readings that good, a leakdown test is a waste of time.
Jerry

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