While i've never had a chance to play an original G3, i own 3 grabbers (an original 75 G1, a japanese copy, & my own home build). I have built a G3 & ripper basses, so my opinion on the matter should be taken as potential truth to it, but not full due to not being full original factory basses.
Ripper: Powerful sound, articulate & big.
Grabber G1: Thicker low mid pbass type kick to the chest. Growls like no other.
G3: Snappier, can sound thick/full using neck & middle pickups mainly. Buck N half setting (middle switch, all 3), can be full with a little cut through in the fold.
It's very different from the other two, worth having in the collection. At some point in the future, i'll build myself one with different custom pickups closer to original G3 spec. Through your 79 SVT, a g3 can sound like a menace no doubt