The block is threaded 1/8" NPT. You can remove the entire fitting from the block and insert a plug.
You are correct that the fitting itself uses what can be hard-to-find parts to connect the oil tube, but the block to fitting threads are standard 1/8"NPT.
If you are using a remote oil filter, you can simply remove the pressure gauge fitting and run the filter directly to the block. The filter uses 1/8"NPT threads. You might need to screw a 1/8"NPT nipple into the block, then add a 1/8"NPT female coupler to screw the filter line into.
Matt
