Nosparks,
If its not too late;
You might want to go to the Lee Precision website (http://leeprecision.com/search.php?mode=search&page=1) and check out the "45 COLT (COLLET STYLE) CUSTOM FACTORY CRIMP DIE" SKU: 80337. You'll end up with virtually the same thing as a modified 45/70 side crimp die. It only costs $25.00 + shipping, and is extremely easy to mod the crimp fingers for our purposes using ONLY a Dremmel Tool. (Involves no cutting of the 45/70 die to a shorter length.) And, also, it seems to be readily available; I got mine directly from Lee in only about 4 days. Hope this helps.