I suspect you can call it any name you want...Les (-:
However I suspect it`s chassis number will have been recorded initially by the MMC and identified by them as a 4/4, and the DVLA will perhaps have that chassis number registered as 4/4 also...? Assuming both the MMC and DVLA have your Morgan registered as a 4/4, then you may introduce a level of complication by calling it by another Morgan related identity...?
In terms of DVLA requirements I suspect the current engine numbers are recorded in the "log book" (V5) which if not, could also create issues in any future claim if your insurance company are not aware of the engine change...?
Perhaps best to keep it simple..?
