Very timely post, I just went through this.

Stay away from OER would be my suggestion. the 3/8" sender I got from them couldn't be inserted as the pickup tube is short and between the float and the sock, the assembly diameter is bigger than the hole in the tank. You have to remove the float and try and get it back in there once the sock and arm are in the tank (easier with the tank out I'd guess). The float also gets hung up on the sock. I tried my best to make it work, but no go. Best I could get was way over full for 20 miles or so, then 1/16 of a tank. I think I got it to work, but then it leaked under the lock ring. Didn't want to waste another Saturday wrench session jacking with it and looked around.

Someone on here recommended the unit from Van's Auto. I second that. The part was cheaper by about $10 and it went right in the hole and dropped right into position. The lock ring design is also superior, as it has a couple of bumps on the humps, if you follow me, that give it a little extra friction and a bit of a lock to lock the lock ring in place. Works perfectly and is calibrated to be at the bottom of the E line on my Barracuda when there is 1.5gal left in the tank.

There's my $0.02

I'm trying to figure out how to get Classic to take the OER sender back.