Very interesting post, Dave. Really enjoyed reading it. I have heard of .25 cal 54's being available in New Zealand and Australia (I think) but never here. Not heard of any .20 cal 54s anywhere. I always thought Diana limited .20 to the old 45's.
I've always thought a nicely scoped & bipod'd 54 would be a great gun. I've thought about getting one often but never have. The accuracy potential of the 54 must be very good indeed. I'd definitely give FTT's a go as they usually shoot very well in smaller bore Diana's.