Just had a look at their catalogue & they only list standard 1,2 & 3 over for model 984 bikes on page 72 for $75us, not sure what the difference is with the model 511/516 pistons other than single rings
They stock new sleeves for the 984 if that helps, page 64 for $120us which would allow you to go back to standard for $195us plus postage
Changing sleeves in CZ motors is the easiest job ever, takes about an hour in the oven from cold at 200deg to get the sleeve to drop out then put the casting back in for the same amount of time & the new sleeve drops in. You have a couple of minutes to align the ports then place weight on top of the sleeve to keep it seated while things cool down
I'll be getting a new sleeve etc for my 400 soon from them