N00B with I'm Not Sure What

Hi All,
Just joined today, living in Ipswich, Suffolk, UK.

Longish story, and sorry to jump straight in with a question, but...
I bought what I thought was a GPX750R as a bit of a project. It was in a pretty sorry state having been turned into a rat. It looked like this:

Over the next couple of weeks or so, it went to this;

Then, this;


I received the V5 for it and found it was registered as a 1986 ZX750-F1. Now this is where it gets confusing. As far as I can tell, this model was only available from 1987. When I search for GPX750R, I keep finding ZX750 results, and to be honest I can't see any difference in them at all.

My problem, finally I hear you say , is that I decided to swap out the airbox with a set of K&N cones. The ones I went for were for the ZX750 1987, but they don't fit. There doesn't seem to be enough of a gap between 1 & 2, and 3 & 4 carb. So I guess my question is, what the bloody hell have I bought?