I have a 436A in my studio that I use on bass quite often.
To confirm what you did with your mods, you changed C4 to 2.2uF -would that be slower than stock? And would .68uF value make it faster than stock? I've always wanted the option for a faster release.
Yes. Increasing C4 to 2.2uf makes slower than stock, decreasing makes it faster than stock.
My unit wanted to thump more and more with faster speeds. Increasing the 33k resistor makes the attack slower and helped it out. I bet tweaking the balance would help with the thumping, but I didn’t do that.
To decrease thumping from fast timeconstants you could swap the sidechain input caps sitting in front of the rectifier tube to smaller values. That´d basically make a sidechain highpass filter.