I don't know if you've gotten your answer yet, but I would assume that grinding down the 510 connection to the same height as the top cap would make it too short.
If you'd like to skip the entire modding process and save your stock top cap you could opt for a few different options:
1. Purchase an Nzonic replica cap that fits the
sigelei 8,13, &19 for about $6 (USD) here
Nzonic Top cap for the sigelei #19b, 8, and 13
2. If you already own a
sigelei 8 or 13, you could switch the top caps out. They are interchangeable.
3. Buy a FusionsMods SG-1 kit for about $25 (USD) from here
SG-1
The last option is my favorite. It will turn your #19 into a true-looking hybrid device and it can be used with many options of RBAs, including your AGA-T.
Hope that helps!