Apart from all the sage advice about oil circulation, to which I would add removing the timing cover banjo bolt A22/1 and squirting oil through to the filter chamber with the machine leaned over hard to the left: I would check that the front forks at least move when the handlebars are pumped up and down with the brake OFF. Drain the carburettors and check the entire fuel system.The front tyre (or tire) looks worn and may have hardened off with age. Also, in passing, the original pressure recommendations for tyres are too low for modern rubber. Please do a lot of reading and get a lot of advice or you will be unjustifiable disappointed with a beautifully designed machine.