If an engine has a crankshaft port timing that's open for 180 degrees (for instance opens at 40 degrees ABDC and closes at 40 ATDC) then it'll have the same timing if the front housing is turned so will make exactly the same power as normal. However I've measured port timings on many engines and there have been radical differences even between engines designed for similar purposes such as CL stunt or RC sport so I doubt there'd be any noticeable power difference so long as the total opening was somewhere around the 180 degrees, maybe + or - 10 degrees or so.