If the original pipe plug is still threaded in the block near the oil filter, you won't get that plug out. You are reading pressure at a good location on the top rear of the block. 100,000 isn't too bad, try another gauge and report back.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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