1250kv doesn't pin down any particular motor, Ken. It simply says that the motor will turn at 1250 revs per volt. While I have little experience of brushless motors I think that you should be looking at motors of around 35-36mm diameter (the first two digits of the motor number). No doubt someone else can add to these sparse details with the rest of the number (length, no of turns etc). "The Other Forum" has a Lifeboats board and I'm pretty sure you will find the info you need on there if you spend a morning going through the postings. **LINK**
You might also ring Adrian at Speedline and see if he can recommend a suitable setup. There's also an article about Going Brushless by John Parker on this very website here if you go to the Home Page and look in the LH column.
BTW I'd venture that any setup which is recommended for say a 1/16 scale Trent or Tamar would also be suitable for a 1/16 Severn.
Take care when buying from HobbyKing that you specify the UK or European warehouse; if you don't then the item may come from ROC and you will be stuck not only with UK VAT and Duty but also a steep handling charge from Royal Mail. Your twenty quid speed controller could easily end up costing you thirty two.

Dave M

Edited By Dave Milbourn on 22/03/2015 09:47:56