Can do it yerself, have enough times. That said, some help never hurts. Sure as hell make things easier.

Consider using a small rubber wedge attached to a wire and put in down between the chain, use it to wedge the tensioner. This will keep the chain from slipping down and make reassembly much easier. Wedge should sit inside the chain and fit snug between the tensioner and the opposite guide rail.

Theoretically the little lip bolted to the block will keep the chain from slipping too far down, but I've found through 6-8 times having the head off of mine that that ain't exactly true. One time I got to go fishing because the damn tensioner popped out and wedged itself against the guide rail.

IF you cannot get the head over the sprocket for some reason, you can remove that little lip thingy. Be damned sure you do wedge the chain if you do that, though. Just wedge it and drop the sprocket down to the top of the guide rails before you pull off the head. And watch your timing marks when you put it back together.