It hasn't gone completely smoothly. I was too chicken to machine the conrods as much as Sonex said initially, naturally I should have had a little faith and saved myself the trouble of disassembling the crank a couple of times until I obtained enough clearance between the camshaft.
I do think that the way of measuring the length of the push rods could be changed though. The book specifies screwing the valve lash adjusters out one and a half turns but all my push rods ended up too short. Probably 3 to 4 turns would work better. Once the push rods are pressed together it is impossible to pull them apart. I set each one up in a lathe an machined off 0.080" behind the ball end. It was then simple to push the end in further to get the right length. It all takes time though.
With the head studs, the best way would be to put a head on without the push rod tubes first so that you can measure the excess length of the head studs all in one go. Then slip the head off and cut them all to the right length at the same time. It will save time frustration and the odd bit of swearing!