Some thoughts on my 100th. B18-B20 rebuild (only seems that way) - we had the same symptoms with our tweaked B18 engine and finally, and after great expense, determined we had an oil starvation problem. We went with a Melling cast iron oil pump that tolerates a lot of abuse and metal.Also had to go to an deeper and wider pan with a modified pickup. Did anyone talk about oil temperature? High temp will cause thinning very quickly even with synthetics. We run a very big oil cooler. The oil temp gauge is the most important gauge in our race car. We also run an AccuSump to give us more oil capacity and to improve supply in tight corners. We also plumbed in a remote filter (an oberg filter was tried but seemed to contribute to the problem so we use a Ford filter which seems to flow well). See if you can't get a used set of B18 rods - they are better than the B20 units. Chey pistons will fit if you go to a big enough overbore and you won't have to cut them; you can even zero out the block and get enough clearance with the gasket. I have used Weiscoes [sic] without any problems. Problems with cam bearings also went away after the changes, and we have had zero problems with the Isky lifters and pushrods even though we run very extreme valve spring pressure ( valve springs were another long and costly journey - we were replaceing them between races at the track until we finally hit the right combination). We tear down after 12 race hours and can reuse the bearings and rings if we choose to. If they would let us run roller rockers, the engines would go much longer. Good luck,
John