I have the 4400 max amps pack. I am actually the first person to get the saddle pack from max amps. I use the BJ4WE and did no modification to the battery tray, however I am using a longer screw on the battery hold down posts. If you go to rc10b4, and search for user 'mattnin' you can find pictures of my bj4we with the 4400 saddle packs.
I added no weight, and I softened the rear end a bit. I am using brown springs and 25 wt oil on a medium sized track, loose dusty with technical jumps.
High Desert Raceplace, Grand Jct CO, Sanwa Exzes Plus Stick Radio, Spektrum,Thunderpower 230g, Modified Tri-Nut Novak GTB2, Ballistic 4.5t 550, 5.83lb SCTE Ten, Novak Sentry Brushless Dyno, Crossweight Setup Station, Junsi 20A power supply Icharger 20A Charger,TP610C, 22B, Novak Edge, Novak 13.5, SC10, Havoc Pro SC XDrive, Ballistic 17.5 Matthew Joseph Cordova