Can I find out what size my engine is from the engine or chassis numbers?

Hello,
I own a 1971 Tramp Roadster beach buggy, registration number NTW 65J,
Engine number 5229078, chassis number 1170460. Due to a massive
breakdown where the con-rod has wrecked the engine I need to put a
replacement engine in. From the above information could you be able to tell me
what engine I can replace it with. The V5 says that it is a 1200cc but my
mechanic is not sure because some of the parts seem to have come from a
1300cc engine