I'm not surprised that the short rod motor didn't do well. That's the sort of change that looks good on paper, but requires almost every function to be re-thought, built, assembled and tested. Remember, this is a venue where builders sweat over "should I use the 5.7" rod or the 5.85" rod in my Chevy " - literally (ratio change of 2.6%); the ratio change here is huge: 1.951:1 drops to 1.689:1, a 15% change.
Shorter rod: less spark, more compression, later IVC, more intake duration, larger port, more port volume, more overlap, smaller LCA, more venturi area are a few of what would need to be reviewed (some changes will have minimal effect, of course). A few years should do it. What, the race is in 2 months? Do the best you can.
There are cases where a violent reduction in ratio works well. Unfortunately, there is a tendency to say "see, no problem - it will work on my Kaiser-Fraser just as well", when in fact it worked because the parent design had too much port and too large a ratio for the displacement (iron Sportster is the poster child), and why big-bore stock stroke Sportsters are notorious slugs.
"they made 200 pairs of them"
I thought that manner of explanation was safely laid to rest after Enzo beat it to death claiming homologo status for half the special racers that left Maranello for 20 years.
They (the unctuous FIM officials) would timorously ask ("please, Commendattore, if it's not too much trouble?") if the required number had been made.
He would wait silently for perhaps 2 minutes, perhaps 3, and then answer "Of course".
Here ended the "official investigation", and off to Le Mans. Henry Ford II's head exploded when he heard this.
Some of those 200 Sportster head castings are still hematite ore in some mountain, IMHO. This is the racing department who couldn't afford to make a special piston, and had to use cam shapes without compensation for the roller offset in the XR because to change it costs money??
Gordon Jennings bitterly commented at the time that AMA appeared not to care that "the factory was playing musical castings".