No oil pressure gauge

Just dummy lights. I put 10w 30 in it to start out with. I figure since it is a little thinner it would "sink in" better after a long sit, then I would put 10w 40 in it after that. It's getting oil so I don't think I need to prime it again, but the low pressure makes sense to me. I guess I can install a gauge...
It doesn't sound like a lifter "tap", like I have heard in the past, more like a knock, I don't know if lifters can make that kind of sound. (I can swap engines in my sleep, I just never tore deep into one before).
When I first start it, it will run smooth (sometimes knock sometimes not) and about 1 min later, it will be knocking and missing pretty bad, but it will idle by itself. I've heard and seen people drop some tranny fluid in the carb to blow it out, then change the oil, but that would just clean the valves and cylinders right?
I'll pull the valve covers and see what I get. Any other ideas for me to try are very welcome!