And a very good point. If done in period with proof why not. Or even if it could have been done why not (ie V8 rover into a MG Magnette could have been done so why not today?)
Having said why not a YB into an Escort? It just needs to be classified correctly 86 vintage engine so if under T&C rules cars needs to be classified as 86 era and rules applied if T&C is your guide/rules.
Now this is why ERC series works well as the handicaps are used as the performance leveler.
If you have rules and are trying to enforce them I tip my hat to you but then enforce them and not one set for X and another set for Y. But I see we are not alone in NZ with these issues it is an issue in all forms of motorsport it seems. Always has been and always will be, as it was as it should be