Looking for recommendations on what brand and type of caulk to imitate the squeeze-out on the firewall.

Also any pointers on technique.

Also looking for recommendations on how to imitate what the factory called "dum-dum", the hand molded wads.

They can be made with POR15 two part epoxy putty. It dries hard just like the original material used to make the "wads,"

If you want it to look right, you need to be and think like a factory line worker.

Step 1: Get really wasted on Saturday and Sunday.

Step 2: Get very little rest for your 4:00 am start time.

Step 3: Apply the seam sealer in copious amounts.

I think the hardest part will be getting the right consistency of the sealer and amount so it will squeeze out. Maybe practice on a couple of pieces of metal to get a feel for those amounts.

Honestly, I try like hell to not remove it, just try to prep for re-paint.
I'll leave factory paint runs in place, too, depending on the accuracy target for the car.
But yeah, a seam sealer that hardens, applied in a hurried/don't care manner. is pretty accurate.