Standard industry practice for an engine of your size/type would be a racor 500 as a primary filter/water separator, then the fuel lift pump, then a screw on secondary, then to the injection pump.
The secondary really does not need to be downstream of the lift pump if that would make it hard to mount.
Where is your filter located now?
Filter heads are available with generic mounting brackets. Get a filter head that fits a common commercial filter like used on CAT, Cummins, etc. Then elements are available anywhere.
Edit: Found this cross reference to Lucas 296:
http://www.wixfilters.com/Lookup/Par...spx?Part=87638
Looks like a secondary already, 10 micron. That is a standard rating for your type injection pump which I think is Stanadyne or CAV.
Maybe what you need to add is a racor primary on the bulkhead.