Further to my post yesterday, I can now confirm the registration number of my Costello was JBB5K. According to DVLA the colour is red, the engine size is 3528cc and KC converted it in 1972. The last V5C was issued on the 6th Jan 2012. The last keeper was dated 12th Jan 2012. The last five digits of the VIN are 83113.
If the owner of JBB5K is known and he/she is willing to make contact, please do not hesitate to email me.