Hi Colin,
If the chassis frame number (the number physically stamped on that front o/s dumb iron) and the number on your bulkhead plate match, then you have an original car. Of course it would help if this same number appears on your V5 document, as this is the record against which your vehicle registration plate has been allocated by the DVLA. The engine numbers are almost irrelevant as engines are changed frequently. If you look in the members area at our cars, you will find comparitively few with their original engines and it only requires a simple notification to the DVLA to change it. Most people don't bother.
If you have two out of three of the above 'requirements' then there are ways around the issue which I would be happy to discuss with you either over the phone or via email.
So to clarify, the number on the V5, ONE of the two chassis plates fitted, and the number on the bolted on dumbiron match. So, for legal purposes, you should stick with this number - be it the '32 or the '34. And it think this is the '32 number - SV18507 - right?
However, you have a choice re the spec. of the car - make it '32, make it '34 or leave the car as it is and simply enjoy it!