You also need a new hose and a stud or two to do the rear head conversion on the front (or the rear in your case), Apex or Tyga can supply a "kit", don't wory about the claims the front wheel will foul the std plug, it's all lies to sell you a £60 plug and cap.
And it is advised to run the .6mm base gasket on the front cylinder if you run the rear head.
But I really would get it back to standard first and running fine. That way you've got something to work from. If it's not standard it puts more stuff in the mix that could be wrong.
If I were you I'd get the rear head right anyway, that needs doing. Some one will have a lower std front head hose lying around, I gave mine away at Oulton, sorry
You'll also need the std rear hose. Ask in classifed ads.
Get the carbs off, check the jets are all std sizes and they're not gummed up, while they're off check the reeds are OK, do the reed block gasket if you're concerned about it, they're not expensive.
Check the power valves are adjusted properly details here and make sure all their plumbing is correct.
A pair of new plugs and some fresh fuel and it should run perfectly, if it doesn't find the fault, coils, stator, dodgy PV servo or whatever.
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