If the damn thing would stay put it may be useful. I guess a Bulldog clip fixed to the comb that would clip onto the head fins and hold it in place might be a good idea. However, slackening off the adjusters and using elastic bands to hold the rocker arms up so the cups are as low as possible makes the job a lot easier. You need to turn the engine over slowly while the rocker box is loosely attached so you can feel all four valves being depressed and then use a torch to inspect the tops of the pushrods because they can (and will) sit on the edge of the cup.
Just used mine tonight.
Slacken off tappets, stick gaskets to rockerbox, clamp comb to left side top fin (with a packer), install rockerbox, position rockers, and check pushrods are in place with a small torch. Tighten bolts and nuts evenly.
Try WWWBSARocketman out in Berwick for a comb. You may also borrow mine, pick up and return at Kilsyth BH
Cheers Peter