I've never heard anything beyond what I heard for the china girls in general, but You maaayyyy run into issues running a normal cylinder with it. See the normal HT's run a 36mm stroke (yes, even the GT5a, measured and detailed by myself), the Super Rat has a 40mm stroke. You could run a bunch of base gaskets to make up the difference but your ports are going to be wacky, and you may even have issues with the piston dropping below your intake port. The SR has numerous different measurements from the Standard HT. The cranks are different, the Super rat has larger bearings, you CAN throw a superrat crank into a standard HT case using 6002 bearings, but the same can be said of most moped cranks in that case, the issue is your gears (if the SR match, great!) and your magneto (you'll need to drill it out and make the mounting hole larger to accomodate the larger crank).
It'll be a pain, and probably net you piss-poor performance (due to the porting anyway), but it should run. If you can, grab a GT5-a cylinder. It's just a shortened SR cylinder. The intake is larger, but the port timing themselves may be off as well.
I messaged BGF right after I purchased and asked if these were actual Super Rat bottom ends, or just replicas.
I doubt anyone would make a replica of a cheap china engine. These engines are actually replicas of some old russian motorcycle engines & Whizzer engines.