White smoke after mild tune up

[Steffan514]

I have a 69 C10 with a 400 CI SBC that I was told came from a 71 GMC, I was doing a general tune up on it because it barely ran which involved:

Replacing a collapsed fuel line that was pinched off that ran from the frame to the fuel pump

Going through the carb which is a 750 double pumper and replacing the jets from 70 and 80 to 67 and 77

Adjusting the timing from 28° advanced to 4° retarded because that's what the book I have says the motor called for from stock

Replaced the plugs with another set of R44T plugs gapped to .035 like the manual calls for.

Set the idle from 2000 down to 750

On the old plugs some of them were white on the face and others were black but they all had completely dark porcelains which led me to thinking they were fuel washed. The last change I've made was the plugs which led to the truck running rougher and making a thick white smoke out both sides of the exhaust so I'm curious if this is a fuel delivery or ignition issue or if I should look into changing my valve stem seals to make sure I'm not getting oil in the cylinders.