Long or short plugs in a 1641

[Elibomrod68]

Hello, giving my brother in laws van a look over... Suspicious that it has the wrong plugs. It's s big red 1641 from the engine shop's. A non classic car specialist has serviced it recently so not confident used correct parts, and not running great. All normal checks done...
I am used to short plugs on my 1600 and this one has long plugs and quick look suggests sooted part way up the thread on the used plug.
Anyone know correct part?
:?:

Cheers
Si

 

[K@rlos]

Depends on heads but after your description I’d say short reach.

 

[Elibomrod68]

Thanks, that's what I thought.
Think I am going to count the threads using a piece of wire.
Cheers
Si

 

[Elibomrod68]

Ended up talking direct to engine shop... Actually looking threads were correct!