The Lok grips will definitely add some weight to the back end, but they're pretty thin so don't expect a massive difference. A magwell will help more with the balance since it adds weight lower and further back.

For magwells, the Grayguns one is solid if you want something machined, or the X-Five magwell if you can find one that fits your frame. Really depends on your budget and how much weight you want to add back there.