Hi Artur,
Yes, your bike certainly looks like one of the early machines that had had their frames replaced under guarantee. It has the correct wide stand and the early chainguard with the pump mounted on it. The brake backplate is also the correct early type with 2 fixing studs for the chainguard.
Douggie,
The full frame number on early machines included the model number - yours should be T35/S/4835/S (that is model T35 with spring frame number 4835, and the final 'S' denotes it is a 'Sports'). A standard Mark 3 would be marked up T35/S/****/3. Later machines in the Mark 4&5 range only had the basic frame number, i.e. ****/4 or 5. Some had a suffix 'B' which denoted it was built with bronze lugs.
Michael,
It might pay you to contact Reg Holmes, the LDMCC membership secretary. Give him the frame and engine numbers of your bike, and see if he can come up with any more information on it. He may be able to establish whether it was originally a machine for the British market or an export machine, and which country it was despatched to. Armed with that information, you may be able to contact the relevant registration authority to establish which numbers it was originally registered with.
Hope some of this helps,
Regards,
Eddie.