Engine smoke, need some advice

[Tomahawk30]

Hi guys and gals,

My 71 Longhorn has a mid-90's era Gen 1 crate engine that appears to be very clean internally. When I first bought it a few months ago, it would puff a bit of smoke on startup, but clear up pretty quickly. I assumed it was valve guides or seals and planned to just get to them down the road sometime. Since then it has gotten to the point that it smokes out both pipes fairly heavily at higher RPMs as well. It has true dual exhaust with no crossover, smokes from both sides, and both sides appeared to get worse at the same time. I did a compression test with the engine cold (would be tough to do warm with the headers making plug access difficult), and all cylinders were between 120-122 psi.

I first noticed the smoke getting worse not long after having the oil changed, and when I had it done I opted for the high mileage synthetic assuming it probably had quite a bit of mileage on it. After pulling a valve cover and the intake manifold, I'm not sure that is the case and I'll probably go back to a Castrol GTX 10w-30 or 10w-40 when I get it all back together. The valve area and the lifter valley were both pretty pristine with no sludge to speak of when I opened them up.

I currently still have the intake manifold pulled (stock quadrajet intake and carb), and plan on trying to get it all back together tomorrow with new gaskets. I replaced the spark plugs this week, and the ones I checked again today all appear to be oily already. Given that it is smoking almost equally from both sides of the engine, would the consensus be that it was likely an intake manifold leak? I would have thought valve guides or seals, but I wouldn't have expected them all to get that much worse at the same time. I also wouldn't expect both head gaskets to go simultaneously.

Am I on the right track with the intake? Thoughts? Sage advice? Horror stories?

Video of the smoke as RPMs increase:
https://youtu.be/q6joCtXns6w

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