Can anyone advise the best way to block the trem on a Luke 3, I don't use it much, do I just put some wood behind the metal block after loosening the springs
You'll have have to raise the saddles to compensate but that's all. Not a big deal.
Do de-tune a little before tightening the trem claw screws. Once the bridge plate touches the body, re-tune. You'll want the bridge to not move when you bend the strings so find the spring tension where the bridge just raises a little when you bend and then add an extra half a turn. Doing it that way avoids too much back pressure on the guitar top which could marr the finish a little under the bridge. If you want to easily get back to stock, keep track and write down how many turns you did of the saddles screws and trem claw screws.