G&P Compression Issues
 

So I have a G&P Magpul Moe
The stock cylinder is tapered and the cylinder head has a crack in it so I ordered an SHS cylinder head off evike.I'll correct the AOR before I close the bx but I was left wondering...
If I change the cylinder head(that's tapered) would it be best to change the cylinder too?

Really, only if you have to. If it seals, it seals.

If it seals, great, don't worry about change the cylinder.
If it don't seal at first, put some telfon tape around the cylinder head and try again. Normally only 1-2 circles, unless you are using super thin telfon tape, then you may need more.
If that still don't seal (not very likely on SHS cylinder head, the only time I seen this was with a crappy stock cylinder head from some crappy brand), then trash the cylinder head because that is the problem, not the cylinder.