I hazard that you may have a bad injector assembly, maybe all three if you are getting that much overage in crankcase. Detroit injector jumper lines are also notorious for leaking, I'd take them all off and look at the flares closely for a crack, also something more common than not. Look closely at the lines just above the flares, and also right at the top of the nut, both good spots for cracks.
One other possibility is the fuel transfer pump. So far as I know, all Detroit fuel pumps have a bleeder drain hole in the housing so that if the seals let go, the fuel runs to the outside, but I've seen some that had the holes blocked with dirt and baked-in crud, so fuel went the other way into the crankcase. This is one instance where you would get a lot of fuel in the wrong place in a hurry.
All this said, if you had bad injectors, you likely would be getting quite a bit of blue smoke and slobber from excess fuel in combustion chamber. If one or more injector jumper lines were leaking, you might see some stuttering or see a loss of power from lack of fuel. A heat gun would tell you quickly if this were the case, point it at the exhaust manifold directly above each exhaust port. The fuel pump leaking most likely would indicate the same way, loss of power.
In my experience, a cracked head into the fuel galley is quite rare though I have seen it, usually on bigger engines. The 353 is a tough little b*****d normally and I've never had much head trouble of any kind with them.
If you are close to a diesel tech school Tom, take the injectors into the shop and see if the fuel systems instructor will test them for you for free, or maybe he will have one of his students do it. Most all diesel colleges have a little pop-tester on hand. Lacking that, find a diesel injection shop or rebuilder close by and get them tested there. They may have exchange units on hand to sell too. You can do a rough test by hand with the injector in a sturdy vise. Place the injector in the vise in an upright position. (try not to let any fuel drain out of the injector from removal from engine to vise) Then use your hand and press down on the top of the injector. If fuel starts dribbling out of the nozzle, you got a bad one. The fuel shouldn't come out till it hits the pop pressure, then will spray. But if the spray is ragged or globby, then you still have a bad unit. This is sort of a shade-tree method of testing, but it does give you an idea sometimes of what shape the things are in.
Lastly, you may have a cracked injector body. This is very rare and about the only way to find it is to remove and test the injector on a test bench. I've seen a couple that were visible to the naked eye, most times they are not.
Last resort is a Detroit dealer, more costly, but very competent.
Good Luck!
