I can readily sympathize with folk trying to build an H15 due to the wheelbase of the front coupled wheels. I have no experience of either the DJH or PDK kits but I have attached some picture of my scratchbuilt model of 330, which was one of five (330-335) rebuilt by Urie from Drummond F13’s, which had an 8’1” rear coupled wheelbase. As far as I am aware there has never been a kit for this particular variant. My model is 4mm scale and built to EM gauge out of a mixture of plasticard brass and whitemetal plus an SEF tender kit. I have cheated inasmuch I have stretched the front coupled wheelbase to 26mm rather than 25mm and used Markits wheels intended for a Black 5 which are the right size but only have 19 spokes rather than 20 as on the prototype. In P4 you could probably get away with the correct wheelbase using Gibson wheels. With regard to drawings all prototypes are covered in the April/May 1994 edition of Modellers Back Track magazine, albeit the drawings are 3mm/1ft so need rescaling for 4mm.