Hello Everyone,
Many many thanks for everyone's help and kindness!! I'm genuinely humbled at the support you are all giving me!!
It does appear that the frame is around the 54 mark from all the snippets of info we are piecing together.
I will have a look at the engine mounts but think its part of the casting, not brazed.
I now know the frame stamping should have 5 digits and a friend has dated the registration number the bike started with to be around the same time.
Last week I had no idea how I went about registering the bike with DVLA, which is a different challenge to building the bike.
Its fairly promising the stamping is under the powder coat so off it will come, so I can start to progress that challenge as well!
Kind Regards
Dave