LOC has the
3.9" ELECTRONICS BAY LONG VERSION + 15" PAYLOAD TUBE as a single item. I've never ordered one, but should have everything you need except the altimeter.
You are aware if you add the DD to the G-Force it will heavier and have to be flown with H or larger motors. Since that is the case, my suggestion would be to consider a similar sized kit with a 38mm hole. I think you will enjoy the larger variety of motors you can use in the L1 range with a 38mm MMT instead of being restricted to 29mm. Even the LOC HyperLOC 835 would be good. It's 54mm MMT, but is DD and comes with all the shock cords and chutes. If you build it a little heavy at 70 oz instead of the advertised 60 oz, it will still get over 700 ft on a baby H like the AT H128W.