I'll throw in my fuzzy recollections. Rip will have to comment on this with help from TK.
I think some of the guys who had been running the bugs at Chemung came to Shangri-La in 1968. Bryan Osgood comes to mind, in Maynard Bodine's Valiant bodied car, which I think had a straight front axle with a big-block Mopar motor. That year, 1968, was the last for the narrower, taller slicks, like on Geoff's #99 white coupe shown above. I think this car was numbered 44 and had been driven by Frank Chapman prior to Geoff taking over. Anyway, the wider, low-profile steamroller tires came in during 1969. Geoff's Valiant was then built over the 1969-1970 winter and debuted that Spring. What a time that was where a person's imagination, creativity, and fabrication abilities, and not so much how much money they had to spend, took them far.