J4 vs JP4 and spark plug conundrum

[ESD1711]

One for all the 16v gurus out there. J4 vs JP4 and correct spark plugs....

So basically I bought my Saxo with what I was told was a C2 jp4 engine. I’ve no reason to doubt that was the case. However, when recently pulling the plugs on it, it seems to have the shorter plugs from a Saxo engine in it.

So either it isn’t a C2 engine and it’s a Saxo one running the correct plugs, or.... it is a C2 engine and it’s running the wrong plugs? Unless there’s a reason for a jp4 to be running the shorter Saxo plug?

Anyways - this poses three questions for me:

1 - what’s the easiest way to tell a j4 from a jp4 without taking it to bits? Assumes there’s a code or markings somewhere which will tell me? Where should I be looking?

2 - assuming it IS a C2 / jp4 engine - what sort of effect will the shorter plugs be having on it? Should it run at all? Should it run badly? Should it pretty much run the same? In my head, the spark being higher up should surely have an effect on how it runs?

3 - assuming it ISNT a C2 engine and it’s the j4 with the correct plugs - what damage do I risk doing by trying it with a set of longer plugs? Ie is there room in there for a C2 plug to fit without it hitting anything?

Cheers