If it's squirting out under pressure as you described, and it keeps pumping it out, that sounds more like an oil pressure or return issue then wet sumping. Since you've already checked your oil lines for clogs and your oil pump is returning oil, you're one step ahead of the game. Here's a couple of things you can check next:
1) The first thing I'd do is a cylinder pressure test and a cylinder leak down test. This should let you know if your rings are allowing too much pressure to blow by them and increase your crank case pressure. If so, cause excessive pressure in your rocker boxes and blow oil past the umbrella valve.
2) Next I'd remove the rocker box covers and look for oil pooling in the top end. That would tell me that an oil return gallery is clogged and the oil is building up in the top end faster then it can get out, and it's then getting pumped out the breathers.
3) While you have the rocker covers off carefully inspect the gaskets. It's possible there's a failed gasket that's letting excess crankcase pressure get into the breather side of the cover, and that's siphoning oil out as the excess pressure goes out.
4) Also, inspect the umbrella valves and make sure they're not warped or otherwise damaged. If so, they could be letting pressurized oil squirt up through.
5) If you don't find the problem in the top end, then take off the cam chest cover and inspect the crankcase breather gear and breather. I think your year is one that used a delrin or nylon gear, and if if it's jumped out of time or a few teeth are worn off it could be letting too much pressure into the cam chest, and at the wrong time.
Other then then the piston rings all of the above are relatively easy fixes, so hopefully one of those will be whats causing your problem.
