Thanks Frank. I had a some conflicting opinions on this, but opted to replicate yours, as I think it is more reliable and one should not really be cruising around with so little juice as to cause starvation on decent. We did ditch the squeeze bulb, but have a small filter between lower tank and pump, then the glass filter a bit South of the vacuum pump.
Funnily enough, when going through the documents that came with the plane, found the bulletin from Austflight suggesting the gravity feed type fuel tank setup. If the factory says so, then....
Sounds like you're running the same setup with the inverted 503, so beware, some more queries might arise, as 23yrs might be JUST enough time to gain some useful insight!
At present, having just discovered the wrong needle jet was fitted, I have regained my smooth running 503, but am now looking at the prop closely (three blade timber) as opposed to the more common four blade fibre, as I'm not sure what sort of climb performance the 503 should be pulling, having mainly flown 582's. Just wish I had the three tubes behind the passenger seat so I could chuck on a 582 and lift some more weight!
Thanks again for your thoughts.