'92 300SE - 110K miles. Been parking it outside for the last several days. Running 10W-40 in the crankcase (maybe 10W-30), and shows full of oil.

When I start the car in the AM (and it's been cold - for Houston) these past several days, I hear ticking from the valvetrain until the oil pressure gauge starts to move. This takes about 1 or 1.5 seconds after the motor runs. Once the gauge moves up to 3 - which is practically instantly after the pressure builds, I still hear a light click-click for a few seconds. The sound is indicative of a lifter that's not fully pumped up.

I'm guessing that the driveway incline (pretty steep - maybe 10 degrees), coupled with the cold, is why I'm hearing the ticking.

Car had a blown headgasket at about 103K and got a full upper rebuild with new chains, tensioner, oil pump, etc. Car runs at about 1.25 to 1.5 on the pressure gauge at idle when warmed up.

Should I be concerned?

It's possible that some debris got into the oil passage to the head during the headgasket job and is now in one or more of your lifters.
This problem usually clears up with time but keep and ear to it for now.
Mike