To my knowledge, the change from M52 to M54 took place when the Facelift E46 was introduced.
For the heavy fuel consumption, check to make sure that all sensors are plugged in - years ago I had work done on the 320i and for a week or so afterwards we noticed a severe lack in performance with very very high fuel consumption! This had me absolutely stumped, but while I was stripping the engine covers off I spotted a plug hanging loose. Found that it was the plug for the intake cam position sensor. Plugged back in and problem solved.
I would clean the MAF sensor with some good quality MAF cleaner - you can also test it by simply unplugging it and see if there is a difference in fuel consumption.
You have the seals from Moranor, so all you now need are the grommets (this is optional but I recommend), the valve cover gasket kit, the Vanos metal gasket, the two Vanos piston bolts (I recommend, these snap easily and may already be fairly weakened). I would recommend pricing these items from the agents and then from other spares places - if the prices are almost the same then probably better to just get the OEM parts.
You will also need a good oxygen safe RTV sealant.