That usually means a Forged Side Relief ( FSR) design piston and they are tricky at best to run in a street application. Good that they are willing to help you out.
I have run Nascar pistons in my 914 for years. My 1st set were a new set of Nascar BME pistons I ran @ .010" cylinder clearance, the pistons came partially finished, I had to have valve reliefs cut & a pin fit, tore it down after 6 months, the piston skirts look like they did when I assembled the motor.
After that I was running one race take outs, some have even came with rings that I ran, The JE's I dropped the cyl clearance to .008"
Pic's of the pistons are used set of SB2 take outs, JE 4.1535"-105.5mm dia for a 105.7mm-4.1615" bore with 2.250", .866"-22mm pins, with about a 1.200" pin height and will be ran with .008"-0.2032mm clearance, giving a 105.702mm bore, and are gas ported. Rings were used that came with the pistons and are .043" top 1.5mm 2nd and 3mm oil.
I checked the end gap on the rings, Top was .019" and 2nd was .025", the cyl's I will have light hone done and run the rings as they are.
These were ran air cooled, one set I ran a year in a daily driver 30,000 miles, I pulled the motor to take the straight cuts out, they were driving me up the wall, the pistons were beautiful. So the FSR's in a more stable water cooled motor, I don't see an issue.
The piston guided rod, is my 1st time, a few of my motors I was going to try it out, but never had a crank or rods cut to try it, so now I am.