Core holes (for freeze plugs) are typically between cylinders, and that one seems to be inline with the cylinder, which would leave little room behind it for a block heater. My 216 has a block heater in the freeze plug opening just forward of #1 cylinder. It's not threaded in, but is an expansion plug type thing.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.