Bolt something straight on the back of it and stand it on end on that, put a 1/4" rod under it and roll it till you find the tipping point. Add the head and repeat.
Then you'd know the CG both ways.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-