Hi guys,

I can answer some of your questions, I have a few "GO" .56 engines and a few weeks ago received some SH .55's as well. The cyl. head of the SH is a drop-in replacement for the GO engine, the only mod required is to drill a small hole in the HS .55 head to fit over the GO engine liner pin (1 min. job). No mods required for the GO head to fit on the SH .55.
I can also confirm that the OD of the SH and GO engine liners are the same, I still haven't completed a whole liner/piston conversion yet to see if any mods are required.
The piston geometries are different, the GO engine has a 23mm/21.8mm (oversquare) the HS has 22.3mm/23mm (undersquare).
A few nights ago I checked the diameters of the ASP .52 (22.4mm bore - validated), Thunder Tiger .50H and Redline.53 (22.5mm bore - validated) and SH .55 (22.3mm - validated).
So - if you have an old TT 50H or RL .53 piston ring, don't throw it away! you should be able to take out all scratches and adapt it to fit on the ASP .52HR (if you have the heli version) - a very useful idea since the piston ring of the 52HR is very hard!
I will continue with my experiments and report.