Rear Brake plate/adaptor

Hi,

Looking to add a rear brake on to a frame with no drilled rear brake hole for emergency stops and also better braking in the wet for use as a single speed rather than fixed.

The options I've seen are :

1. dia-compe kit which includes a set of plates/brackets and their own brand brake caliper -https://www.velodromeshop.net/brake-calipers/dia-compe-rear-track-frame-brake/
   
2. Kimori brake adaptor - https://www.bricklanebikes.co.uk/kimori-rear-brake-adaptor
   
3. Tempra hidden brake system - http://tempracycle.com/?pid=38432394
   
   

Has anyone found any other options?

Tempted to have some plates made and just use my 105's from another bike? Tempra also have plates/brackets but don't seem to be available in the UK?

http://tempracycle.com/?pid=36455155

Though surely these are easily machined by someone knowledgeable enough?