Techron's about the best cleaner you can run through the injectors. For a better clean you really just need to send them in for servicing... the screens should be replaced and the injectors utrasonically cleaned. Generally, you'll pay anywhere from $10 to $20 each and that includes replacing screens, ultrasonic cleaning, testing for leaking and flow testing (so you know if you've got a bad apple in there somewhere).
I would not try brake cleaner in them... nor any other flammable solvent, you have to supply electricity to the injector to open the pintle; apply for too long and you fry the coil; create a spark and you're going to be waiting for your hands to grow back.
It's definitely worth getting the valves lapped, valve stem seals replaced and shims replaced as needed for proper cam clearance while the head is off. Also have the head vacuum tested and inspected for any signs of cracking.
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