If the engine turns over without hitting (I'd assume so if it ran) rotate to TDC on the crank BEFORE doing taking anything off, makes it less likely to bend valves while fiddling with the cam position.
Remove rocker cover, look at your marks to see if it really is out.
Slacken the tensioner, being gentle with it as they tend to break if forced. Bit of gentle pressure down and twist (counter clockwise I believe) and it should spring back up freely.
Loosen off the cam bolt to allow some room for the sprocket to wiggle on the end, makes it a bit easier to get the chain off. Be careful with the cam dowel pin because if it comes out and drops in the sump you're royally screwed. It shouldn't if you don't try and completely remove the sprocket repeatedly.
Time your marks based on the cam and crank with the Dizzy, not the sprocket and chain, as that's how I f**ked my timing the first time I did it and bent valves.
Use this thread as a guide to your marks:
http://www.ozgemini.com/forums/tech/vie ... hp?t=14426
Make sure it's not the ignition timing too, which is also why I say check the marks are off before taking anything apart.