Here is my 007 with SMC 4000 lipo installed in it with the ezmount
I found that the wieght was too much to balance the chassis side to side so I took a 1/2oz off it.The I added weight to the centre of the chassis to bring the car up to min wieght.{they will be checking at my track}
The SMC 4000 pack is 20.5mm thick and it fits in the car well just had to grind the bulkhead a littleand the battery strap had to be shimmed up.5mm.The ezmount worked very well, the inserts lock the battery in the chassis.
I find it very surprising you were off balance with the 3.0 oz weight and 1.2 oz under pack.
I do have a 2.5oz fixed weight that may have worked better in your case. I'm not sure how that can be, most 007's I've seen require some additional weight along with a 15oz+ NiMh pack. You should only be around 13oz or so right now...possibly less since you took some off.
Did you put the optional lead weight inside the slot or leave it out? Also what motor are you running?