Hi.
What the heck is an eck???
If the neck heel is thicker than the original, that happens. Without seeing the pair, I'd guess that's the case.
The remedy is easy, You can thank Leo for that, just place a shim on the front of the neck pocket.
People are used to shim the back of the pocket in order to lower the action, but there's plenty of questions if the opposite is possible.
It is, it just doesn't look very good, with the gap and all obviously, but that's the price to pay for not-so-interchangeable parts.
Usually, if that happens, and there isn't any $2000 markings on the neck or the body

, a few passes on a mill or with a router takes care of the problem.
If the resulted increase on the sustain is a problem, one can gouge either of the parts for less contact area if so desired.
Regards
Sam