You could take the bars off the bike, clamp them in a vice and connect that to the engine again. You need leverage and the clutch plates could be seized too. At the moment you need to get the barrel off so if it is too much grief to mess with the clutch then I would concentrate on getting the barrel off by the heat and plusgas method. This will allow you to jiggle piston as you try and engage gear. Whatever you do, I think that the engine will need to be split to change the bearings and seals if you intend to ride it.
They are never going to be worth the money spent on them. This doesn't stop me but will stop a lot of other people working on them. To strip and rebuild the engine you are looking at around £300 in parts (in the UK), that would include bearings, seals, gaskets, clutch, rebore and piston kit, crank rebuild and oil. Add £150 for wheel, steering and swingarm bearings, seals etc. £100 for tyres and tubes. £60 for chain and sprockets. £20 for a battery. £50 for new cables. That is £680 however you have a bike that will still look cosmetically challenged and that assumes that nothing else needs to be replaced. Even the basic, rub down and spray will come in at £100 but if need/want to have the tank rechromed it would be closer to £500. If you need to have the wheels rechromed or stainless rebuild, that is another £400. If the seat is knackered you can buy pattern ones for under £150 delivered and should just leave the exhaust. Mine is basically shot and I haven't found a decent one anywhere on the world - believe me I have been looking. When I get to that stage I have almost decided to get a stainless one hand built, probably another £400.
These are my estimates based on my bike, yours may be in a lot better condition. To do mine up to how I want it will be around £2500, it will never be worth anywhere near that in my lifetime or possibly ever. Bikes are my hobby, not my business.
All that said, you could get a few basics done for a few hundred pounds and run it how it is. It may be the time to throw a few pictures up of it.