I would always expect comebacks if data is incorrect.

Remember that it is your legal duty to inform the necessary authourities of any changes or alterations, and ignorance is never accepted as an excuse.

No reason to draw attention to yourself by knowingly having diferent data registered 

[My Youtube channel]

Absolutely make sure you give the insurance company all the correct information regardless.
(and yes no reason why the V5 can't be correct for the engine/colour)

As for whether there is a variation on the V5 to what is the buggy is...
Well without saying any more (let you read between the lines)...
You insure the vehicle with the insurance company as a beach buggy regardless of what the description is/may be on the V5. 
(and that statement I got from a certain insurance company)

I think I'll just buy a Ford Focus  , so here's the plan of action if I buy buggy, 1. Hand over large sum of hard earned/ 2. Insure buggy with correct engine size/ 3. When I receive v5 in my name, give a week or so then send V5 off stating engine change/ 4. Drive it like I stole it....all agreed ?

Personally, I'd never dream of selling a car that wasn't 100% correct on the V5C and I can't understand anyone who would.

[My Youtube channel]

I think I'll just buy a Ford Focus  , so here's the plan of action if I buy buggy, 1. Hand over large sum of hard earned/ 2. Insure buggy with correct engine size/ 3. When I receive v5 in my name, give a week or so then send V5 off stating engine change/ 4. Drive it like I stole it....all agreed ?

Agreed.... Though I would probably insert point 4 before point 3 

I think I'll just buy a Ford Focus  , so here's the plan of action if I buy buggy, 1. Hand over large sum of hard earned/ 2. Insure buggy with correct engine size/ 3. When I receive v5 in my name, give a week or so then send V5 off stating engine change/ 4. Drive it like I stole it....all agreed ?

Agreed.... Though I would probably insert point 4 before point 3 

   

Our beetle 1300 is that on the V5 because 4 years ago DVLA were going silly on engine swaps but it is insured as a 1300 beetle with  1584cc motor thus the insurance is correct, engine size on historic makes no difference price wise but it needs to be insured as exactly what it is.