No 228 was the last of 4 "Q"s introduced in 1936 and was followed by 2 more in 1938. Their radical design (for the day) with the engine behind the front wheel and partly below floor level was not a commercial success and the Christchurch fleet was both the largest export order for AEC and longest serving fleet of "Q"s anywhere in the world.
The THS actually has both 225 & 228, plus the chassis of 227. (Apparently 225 had been converted into a motor caravan/motor home). The intention is to restore 228.
Refer also to "On the Move", volume 8.