Thanks shooter.
So I've just measured the lift on my block without the head fitted. Just from the pushrod and the pushrod is moving up by 7.1mm
The depth of my chambers is 7.3 on average, so as much as they won't hit I don't want to run such small tolerances in case of valve bounce. So inevitably they'll definitely need sinking.
I called around today to different machine shops but nobody seems willing to want to do it.
Have you taken into account the rocker ratio? which will be a minimum of 1.23 if you are using the A+ type rockers upto around 1.27 if you are using the big pad pre A+ big bore version. This whole set up is what I call fighting you, as in you are getting problem on problem. Keith Calver recommends the head gasket thickness as your safety barrier in these situations.
Shooter
There's also circa 0.040" (1 mm) to be 'gained' in the head gasket thickness, moving the valve further away from the block.