i didnt like the GP mounts either at the beginning,

now i would say about GP adjustable mounts they are not the cream de la cream but not the bottom of the barrel either.

its easier to mount them, the two piece mount like if you are missing 1/2 mm plus or minus then its hard to fit the motor snag.

dont dismiss them you will meet them in the future, they are easy to mount engines on and easy to get and they are cheap.

sure there are planes that will not accommodate them or they are not fit but find how to work around it.

there are two piece sig glass filled motor mounts, they are cheaper and come with the hardware but then you cannot replace them with other type of mounts so you buy several.

use the method chuckW mentioned thats the way to go.