timing problems again...

Hi Folks, I'm having problems again: Here is the conditions my 350 SBC (mostly stock) is having:
1. Timing: the engine doesn't care what I set the timing to. Everything between 20 and 50 degrees will work, between 25 and 45 the engine runs at the same RPM producing the same vacuum (doesn't run all too well, but OK).
2. My breather cap pumps out oily fumes. PCV is installed and new, valve not blocked and if I rev the engine there's a lot of fumes coming out.
3. front seal (renewed for the second time) loses oil. It's installed correctly, balancer is new, too, so there are no rough edges between balancer and seal
4. poor fuel economy
Can it be (someone guessed that) that my piston rings are badly installed (engine was newly rebuilt by the previous owner, but not specially well) and thus the blow by can't be handled by the PCV and produces too high pressure inside the block, pushing oil out the front seal?
How do I find out whether the blow by is past the rings or past the valve guides?
How can I test whether the rings are properly installed without taking the engine to pieces?
What else could it be?
Slowly I'm thinking of buying a new engine, only having problems with this one :confused:
I appreciate any help I can get, thanks in advance!