67 727 trans in my 72 duster, 3 prong neutral safety switch help

I have a 72 Duster 340 that had a 727 trans in it that has PK2801542K 2392 9273 stamped on the drivers side pan rail. (I bought it that way) It decodes as 67 727 for 318 and my 3 prong neutral safety switch does not work in it for the back up lights only. I did fix the wiring so that all checks out now. (another issue that I dealt with in previous posts) and the switch works to turn on the back up lights when tested but not when it is in the tranny. I have since read on here that the switch was changed to 3 prong style in late 1968. I have heard on here that I need to change the comb to make it work. How do I do this and does anyone have the comb for the later style 727 that i need or can someone tell me where to get one new? (junkyards here are not a good choice as the ones I know of here have their cars buried in mud and all sorts of overgrowth.)