There are still block heaters that use pipe threads, but most I've seen would go quite far into the block and may not have room at that location. The ones that go in a freeze plug hole are usually a bent pattern and wouldn't work on a threaded hole. Here's one that might work there. Link


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.