Hi Joseph,
I thought I'd better check my statement above (before anyone else did) and sure enough – there is at least one 0-4-4 2.5" design published – and that's LBSC's SR 0-4-4T.
The drivers are 2.75" ( 70mm = 5' 2" at 13.5mm ) and its a slide valve with slip eccentric motion. Boiler is meths fired water tube. Published in English Machanics 30th June 1944. Photo copies of the construction notes were available from the 2.5" Association at one time and probably still are.
Regards,
Ian T