I would venture to say ST60's are like a box of chocolates...
heh...(It's almost as bad as asking one of the Fox Racer guys what is the exact dimensions of a bone stock Fox .35. Know one seems to know. )
The ST60, like the Fox 35, seemed to wander around the map quite a bit over the production cycle. Some with thin sleeves, thick sleeves, chrome, no chrome, muffler bosses, no bosses, standard loop porting, PDP porting ,56 with 60 cranks, 60's with 56 cranks. I never cease to be amazed when I open one up. I've stockpiled enough parts to keep my various versions running, whatever they may need, heh, which is always one solution.
I've got one ST60 from several years ago that I jokingly refer to as "Franken-Tigre". At the time, all I could find were the longer con rods, so I used one. I figured, " what the heck, why not"?. It also had a bigger boss on the lower con rod crank pin hole, so I had to dremel out the case a little for clearance.
It had the effect of dropping the sleeve timing with the longer rod, and I had to use a lot of head shim to get clearance to the piston top. BUT.... you wanna know something? It's turned out to be one sweet running little monster. Deepest 4 cycle I ever heard out of a ST60, likes super low RPM and will swing a 13x6 in heavy wind without windup.
Sorry to ramble, enjoy your Tigre, they are fun motors and most all of them run decently enough if the ring not worn and is installed properly.
EricV