I'd recommend the 50MT starter, which was also used on the later models. The 12T pinion matches original pony pinion.
I only know of individual block off plates, don't think they ever offered a kit. Most folks make their own.
Hi LJ,
Ran across this on Ebay...might want to check it out...http://www.ebay.com/itm/NEW-50MT-PONY-MOTOR-REPLACEMENT-STARTER-24VOLT-24V-CATERPILLAR-D7-D8-D9-/110922514286?hash=item19d37f3f6e&vxp=mtr
Johnstone