Finished priming the oil pump and was just about to put the new plugs in my rebuilt 292 when I noticed that they were clearly the wrong ones.

I bought Delco R44T - which is supposed to be correct. It's also what the core had installed when i bought it and sent it for rebuild.

However the holes are quite deep - an inch perhaps - with only the bottom 1/2 (piston side) threaded.

Interestingly, I happened to have R44XLS plugs "sitting" in the holes to keep things clean while she's been waiting - and they do appear to be about the correct length.

This is odd, because the XLS plugs came from a mid 60's 250 head, and as I recall my previous '84 292 did in fact take the 'proper' R44 tapered.

I know my head is later model because it has the A.I.R. ports at the exhaust.

However - it does have what appear to be torx head bolts which I've never seen on a 292.

Might I have some oddball head - maybe marine or agricultural - that requires a different plug?

Clearly I can't use the recommended plug - it's way too short and only engages a few threads.

Should I just go with the long R44XLS gasket plug and hope it runs well?

Any help appreciated.