I'm not sure I understand... you mean the copper coming out of the coil I'm guessing? I think I'd yank that out if you have something jammed in there and just clean up the hole. My thought is that you've gone this far, make sure you have a good connection to the coil no matter what you have to cut up, then solder, then insulate.
I think the RTV I used was rated much higher than that, but it would seem like 400 degrees would be enough, but I'm not sure how hot the coils get. I think the plastic would melt close to or much beyond 400 degrees so I think that might be ok.
As for the JB plastic weld, I've never used that before. I'd say make sure you have plenty of silicone or whatever insulator you use on there when you seal it back up. Doesn't have to be pretty since it hides out under the tank anyway, but make sure you get that connection set as good as possible.
So, in summation, connection at all costs is priority 1, then insulation as much as it takes. Go a little thick or spark could ground to the frame.
Good luck.