The G force does not save you all that much money over a TKO. By the time you buy the upgraded shaft, and pay for gear installation the price gap is closed considerdbly. And if you don't have them do it, expect to pay someone else $350 to do the labor on the trans rebuild.
IMO got with a TKO 500. Expect to shell out around $2300 by the time it's done with clutch, maybe a few more bucks.
Reason i say 500, is because i'm not a big fan of the 600's gear ratio options. I speak from experience on that.
In fact, i just looked at the g force page, they want 2,000 for a built g force used core, or $1500 for parts and $250 for labor.
That's the cost of the tremec, you'll just have to buy a new bellhousing and yoke.
I wouldn't mind having a g force setup, but i would mind paying 2 grand to get it.