Have a p220 with the e2 grips from the factory. Have been thinking about getting a set of wooden Nills grips.

I know you have to change some of the internals for the e2 grip to fit since it fits a little bit more snug to the gun. If the gun has those e2 internals, will they work with a set of standard grips?

I believe the only part that is different with the E2 grips is the hammer strut and spring. It bends in a bit to accommodated the profile of the E2's. Since this provides more space than less, it doesn't need to be changed. If you were going the other way; that is converting a standard panel grip gun to the E2, you would need to replace the hammer strut and spring. You will of course need 4 grip screws.

That was my thought as well, I just wanted to verify.

FWIW -  I replaced the standard panels on my M11-A1 with the E2 grips and I thought I had to replace the strut and spring. Since I'm local, went to the SIG Pro Shop looking for the parts. they told me my pistol is of new build and there is no need to change the strut and spring. Took their advice, put on the E2's and no problems.