Just built a pair of chambered mufflers for a neighbor who is almost finished with a '62 Polara wagon & has a freshly rebuilt 440. The dual exhaust was custom-bent & when the engine is running, milky-looking oil starts flowing through the LH bank of the exhaust - comes right out of the tail pipe. After things heat-up, the LH bank starts with the oil smoke. Motor sounds & seems to run great. Any ideas what might be going on? (RH bank is fine - no oil coming through the exhaust).

Any ideas? Oil getting past the rings on the LH bank?

If he had the heads ported they might have ground into the water and oil passages. He also should check the radiator, and oil to see if there is an oil/water mix in the radiator, and oil pan. Or a crack in the cylinder wall or combustion chamber of the head, or valve seat. Maybe do a leak down test on that bank. With the pistons at both top dead center, AND bottom dead center, if you can be sure the valves will be closed at BDC on the power stroke, or near BDC.

You can drill/tap the stat housing for 1/8 NPT (easy to do) then screw in a schrader valve (Oreillys has it as a "tank valve", less than 3 bucks) & with your air chuck pump it up & see if it holds (15 psi max) & it will reach that FAST as it ain't like airing up a flat tire. EDIT best on that plan is to also get a 1/8 NPT triple female nipple and a short double male end nipple and a gauge that will go to 20 psi or so (I see cheap ones that are 15 psi) & plumb it in to the stat housing so you can (easily) watch the gauge as you pump it up then watch to see if it drops. the plumbing pieces are dirt cheap at your hardware store & grab some teflon dope or tape. MORE EDIT plumb it in the block port for the water temp sender so no drilling/tapping needed.

This approach works as well. Probably a water/oil mix that turns to steam as it warms up.

post when you find out where its coming from.

You could look at the spark plugs to start

I will - I'm curious as hell myself now. Took over a pair of 20" resonators for him tonight - the chambered was too aggressive for him, so he'll add the resonators into the tailpipes to mellow things out some. I placed all the comments so far into a Word document & took over to him. We looked into the radiator & that looked fine, also no water seeming to mix into the oil either at this point - looked good on the dipstick. I'll be gone for the rest of this week, so he's going to dig into this with his engine guy. I'll post more as I find out more. Thanks so far.