I've been fitting a Paul Goff supplied filter, it sits nicely in the tool box with the pipe work being routed between the battery and mudguard. I have retained the armoured oil pipes to the engine and made return side connections with off the shelf 1/4" BSP fittings from local hydraulic supplier (Pauls kit assumes using new rubber hose to the return side)
Finally got round to filling up and testing yesterday which gave a nervous couple of minutes running the motor until oil emerged from the return pipe, I had tried to get circulation by turning the engine over on the kickstart (plugs out) but no chance. I had filled the new cartidge with oil but I suppose there's a fair bit of pipe to load up on a dry start.
All in all it looks a good solution to give improved filtration and is, at a glance, an invisible modification.