I haven't done a 6 one, only 8s (but imagine same problem applies), but from what I understand of your problem you need to be able to hold the cam level so it goes smoothly in (very tight through bearings). To get proper control (ie be able to lift nose in far end of engine) you either need the Holden special tool, or on the 8s that I've done, I use about a foot long bolt that fits in the hole at the end of the cam (end you're holding onto) and you'll be able to hold the cam horizontal with it and get better control to fit it through. Also take dissy out if you've got that in (6 runs off cam doesn't it?) the gears may be impeding it