Hi TF,
More information is necessary here. You didn't indicate which model bass body and neck you're wanting to use.
4 string straight headstocks can be reamed for GB7s. You'll see that here:
http://www.warmoth.com/bass/necks/necks.cfm?fuseaction=standard
Tiltback headstocks are already drilled for GB7s as are several of the Deluxe 5 necks.
Warmoth does not carry Hipshot tuners. As such, we do not track all of their current models and dimensions. This is where you'll need to determine which model you want to use and see if it fits any standard tuner reams.
Hipshot A (17.5mm and 19.0mm string spacing) bridge routing can be done on the Gecko 5 basses though it is non-string thru.
HTH,
Eric.