The plug must be about or over 5/8" long is my guess.
So drill and tap 3/8" and use a slide hammer, no chips in the oil if you don't drill through it.

Grigg

Last edited by Woogeroo; 03/02/2015 1:16 AM.
•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-