sending unit replacement

Ditto RedFish. You always have to tap the ring a bit to center it, whether factory or after-market. I usually have to bend the lock-ring tabs to stick out a little more to keeps it tight after it settles in the grooves. Coat the lock-ring with a little oil and it will slide in easier.

superdart, that is a nice-looking setup. It looks like you have a fitting for return line, which makes future EFI easier. Smart that you are using "fuel injection" type hose clamps.