I installed a block heater in one of the core holes, but haven't plugged it in yet. For the cost of the block heater, I wouldn't use them in place of normal core plugs. A guy could do that for 3 of the 5 core holes, but not the two on the rear of a 216. The cam would interfere with the one at the end of the cam, and both would prevent the bell housing from mounting flush with the block.
