I would doubt that you can get enough 1680 into those .38 Special cases to hurt anything. I use around 18 grains of it in .357 Max cases under a 212 grain Lyman RNGC or 200 grain Remington jacketed bullets in a rechambered H&R. That's close to a full case in the much longer case.
I would suggest you see how much powder is a full, but not compressed, case with that bullet. If it is around the 12-14 grains I think it will be, you should be all right.
Pat's Reloading and Jeff Barlett both sell the surplus version at very attractive prices, somewhere around $64 for an 8 pound jug.