If you don't have a PCV valve, you should have at least a road draft tube set-up.
When I first put the Webers on my Pantera many years ago, I didn't have any place to plug in the PCV valve, so I just put on two breather caps and let it go. Not long after that, I noticed my engine was building up such crankcase pressure that it would pour
oil out the rear main at idle!
I fashioned a road draft tube set-up, and attached it to one of the breather caps, and the problem went away.
Regards,
Jeff