Quote Originally Posted by xboxrox View Post
My engine is still using plenty oil even after installing a new cylinder head ~ oil ruins catalytic converters ~ maybe there is a way to help piston rings seal (soak Marvel Mystery Oil into the cylinders..?)
How much oil is it using? Is it as bad as (or worse than) before the head replacement? Does it blow blue smoke all the time, or on start ups and mostly when accelerating from a stop? If it's a serious issue, best to address before worrying about the catalytic converter.

If the consumption is excessive, do a compression test and maybe a leak down test if the compression test results are concerning. If it passes these tests, the rings aren't the issue. Maybe they used low quality valve stem seals on the new head. Bad seals won't affect compression readings, but they will increase oil consumption.

Regarding your questions about the manifold and converters removal, I don't know for a fact, but it looks like there's room to remove everything together. To separate them, use plenty of WD40 and an impact driver. Hopefully they're available at Five 0 Motors.

If you do disassemble the manifold and cats, why not give the lower cat the same "treatment" as the upper cat? It would save the cost of a new lower cat. Or alternatively, why not get a set of Pacesetter headers which are about as costly as the lower cat? Both options aren't EPA compliant, but neither is treating the upper and replacing only the lower converter.