Well, if your reg is stainless, or chrome- or nickel-plated brass, then yeah I'd probably grab it. If it's bare brass, WE CO-3 at a welding shop will cost $4 or $5, and is exactly the same as the one you have, but half an inch shorter.
To reinforce what Taco said, though, make sure the reg will clear the cylinder. A standard torpedo-shaped body with large gauges needs that extra half inch. I have a Concoa 212 and GO CYL-20 which have that issue, and I have a 2 1/2" brass nipple on one of them, and a 2" stainless nipple, plus a 1/4" stainless street coupling on the other. Without the extra length, the high pressure gauge actually touches the knob on the top of two different cylinders. I'm assuming you don't have this issue, but I figured I'd mention it just in case.