I went through a similar issues with a leak on a Toyota many years ago. I tried to perform a gypsy fix, but I ended up pulling the front cover and fixing the leak correctly, so I didn't overheat and trash the motor.

As others have stated, please take the truck off the road, pull the front cover and install a new gasket. While you are in there, go ahead and install a double roller timing chain and gear set. Please don't waste time trying to perform an alternate repair when you can just use that time to fix it right.

 

if you got the water pump off i wonder with all the timing cover bolts out if you can possibly move the timing cover enough to either slip a new gasket in there or squeeze some rtv in there? could maybe try the egg yokes in the cooling system to seal it

 

Jb weld makes a lot of different epoxies, I'm assuming you guys used the stuff that most places carry witch is a general use epoxy. You might try this one it's for temps up to 300* Again this is just a band aid until you can do it the right way. If you went as far as you did i would have rented a puller and any other tools you need to do it the right way. It's a lot of wasted time pulling everything off just to put on a band aid.
https://www.jbweld.com/collections/w...ld-epoxy-putty