L4 Bren Ejector Block, 7.62X51, *Good* - Bren - Light Machine Guns - Machine Guns
Watch what you wish for. Any conversion for the FAL mag entailed a lot of work. In addition to the receiver machining for the mag and ejector block, the mag stops in the the receiver were almost completely removed. The Enfield conversions added plugs to reinforce the mag stops.
When you were done you only can use 7.62 Nato. With the conversion under discussion you can switch back and forth between .303 and 7.62 easily.
Try different thickness shims in the rear of the ZB39 mag. per the pic. Just slip them in until you get the right fit then soft soldering will work and won't screw up the mag.
Joe