Wrig0335,
The aluminum backplates are those used for the OS .15 FP. It is a tiny bit shallower and you will loose about 200 rpms with them but the gain in reliability is well worth it. Here a couple of folks have had great luck wrapping teflon tape around the backpate then reinstalling it. Socket head screws are bad on the backplate because of their narrow head diameter they can pull through the plastic. If you use socket head screws on the backplate put a washer behind them to spread out the load area. Good luck. By the way are you getting any bubbles in the fuel line? The OS LA needle valve assembly is excellent but it can leak.