Replacing Boss kit/hub with stock wheel (pulling my hair out please help!)

[Wonga Spar]

I'm trying to remove an old momo steering wheel to replace with a Celica one. I've got the wheel, airbag and adaptor, but when I pull the aftermarket wheel off I'm looking at some adaptor plate (looks like a works bell hub/spacer(?) and it absolutely won't come off. 

I have poured over guides/videos but what I have on my car doesn't match any of them, which suggests I'm missing something... please somebody tell me how to get this metal plate off, or what I need to buy to get this celica wheel on

 

Any help hugely appreciated, I'm going mad here.

 

 

Edited May 21 by Wonga Spar (see edit history)

[Style]

Have you given it a real good wobble and pull with the wheel on the boss? The splines are a snug fit when putting something like that on and it provides a lot of contact friction. So it might need a bit of persuasion to pull it off. There may also be some light corrosion thats bound them together a little as well.

As far as I'm aware, it's just a central nut that holds that in place which it looks like you've zipped off. So it should be free. Hopefully it's not a case of chewed splines from the boss having a slightly different pattern or something

Edited May 22 by Style (see edit history)

[Wonga Spar]

Ive persuaded it as much as I dare unfortunately. I've done all the tricks, bashed it, soaked in wd40, put the wheel on and yanked, I'm not a strong man by any stretch but I can confidently say I've given it more than enough force than it should need. Really worried about damaging something if I get any meaner. 

[jagman]

You have to use enough brute force so it flys off and hits you in the face