Hello all,
The method I use is pretty easy to get the push rods in, especially using my soft copper gaskets, firstly put the gaskets in place no need for any sealant, clamp the large gasket to the head using the comb & welding mole grips, that's the ones with the flat jaws, make sure that the two holes match up, put the push rods in place, turn the engine over so that the rods are almost equal, gently slide the rocker box over making sure you get the central web in the middle from the front, lower onto the head, checking you have captured the rockers on the way down insert the first bolt, middle, then put the others in, remove comb, job done.
See attachment.