I know nothing of the gsr timing belt personally, and its possible a b series belt could work...
the h23 and DOHC f22b belts are not the same... The h23 has one additional tooth, but TOOTH spacing is the same... Thats why you use them... When I got my f22b the instructions and demands from the importer said to the use the h23 timing belt... Believe me, we inspected it over and over again... It works... You just have to tighten the hell out of the manual tensioner...
To Blk89,
Yes, I have a boosted h22 in my 3rd gen... Theres a thread with some pics of it I created in the 3rd gen forums... Its kinda camera shy, but for good reason... Ill let you know what it is once I figure it out...