Here's my factory experimental YZ80 piston cast with advanced tranfers. Sort of the opposite to what we're talking. Just copied my pics off here as easier than finding where i put it in the shed lol. 
Found a better side view. 
Found my RT1 piston i ran in the short stroke 360--325. Search engine on here works well. I probably decided to go high up on the skirt to avoid weakening it further down. In hindsight was a brave [ie stupid] move lol. Worked good. 

Shyted--you mentioned a KX reed cage assembly. I think i used one from a "78 KX125 with fiber reeds i had 'under the bench'. By memory its 6 petal & the mount holes are in a bit had to cut half the circle off each hole then sit something out around the 4 mount bolts for it to pull up square. Moving slowly along the vide dragging it, it looks like i have nothing in there like a gap so i don't know. Was sealed up anyway. I'd run out of 360 reed cages at the time. Mind you they're the same as the 1980 YZ80G cage. Only slight difference is the cage bars where the reeds shut are shaped a little for better flow, nothing much really just identical except for that.
www.partzilla.com/catalog/yamaha/motorcy...0/yz80g/intake-yz80g
Not sure if this double reed cage would fit or something like it as shows more below in the listing on ebay.
203372625553

I just thought. I could get a copper gasket twice as thick and reduce the compression ratio. That would have a similar effect as a shorter conrod . The exhaust port problem would still exist though.
Facinating pictures of the pistons.
Interesting stuff Mark and there was an era not too long gone where people like you could challenge factory runners. The road racers Graham Crosby and Kenny Roberts come to mind. That was Roberts with Kell Curuthers tuning his carbs and engines .
I'm going to try and pick the 2 stroke book up.

I still have my copy I got when I was a kid...  probably about 1975. 

Jimmy Johnson...  NASCAR legend today...  was in one of the big team cars at the LA Coliseum...  he went a little wide in the corner at the top of the peristyle jump back into the stadium, I dove inside and held him off for the remaining half lap to take 3rd place from him.  Boy was his team owner angry.  His goal was to always win 1st, 2nd, and 3rd and I messed that up.  He protested everything he could and I was held in impound until the start of the main event.  Had no time to prep.

The team Jimmy Johnson was driving for used to put brand new tires on for every heat...  BFG Radial TA street tires that were hand grooved...  worked really well on the special clay mix tracks they used to build the stadium tracks.  I used to grab their take-offs out of the dumpster (with permission of the BFG guys)...  I couldn't afford new tires...  when team owner found out he demanded BFG saw the tires in half before throwing them away.  

I had a lot more fun at the smaller and desert races...  we helped each other out and there was no TV or big money teams acting like jerks.  Except for the 24 hour endurance race I won but that's another story.   

Wow MarkT that’s awesome congrats I’m proud for you. Tell us your story about your win at the 24hr can’t wait 

No!!. Double head gasket in no way relates to a shorter conrod sorry. Well ok it would reduce compression for sure but have other bad affects. Whole new story there. IT490 came with double head gaskets & washers with reduced hole in the inlet where the carb fitted in to tame it down, which it did. But still had more than enough power.

MarkT great stories. Be neat if you had a link to videos of your time racing. I'd be glued to it for sure. Keep the stories coming.

RT,check out Micou Meekoo latest YouTube clip. I found it at 07.30 this morning. Stranger things and what have you!

Can you give a link easily. I just youtubed him & found an RT1 from 9 days ago but nothing out of the ordinary. Cheers.
Man he does such clear videos. I'm hooked.

Look at how many gaskets he put in to lower the compression . Listen to his bike on the over run after that and watch the handlebars etc,no jerking around or any of that horrible "chunking" from the motor.