Power Steering -again!

I have a 70 Valiant hardtop -a Dart with Ausy Hemi 245 and I want to improve the steering - It has all components new and a rebuild power box. It runs about 2 D positive caster and is actually not bad ---but very sensitive .
Reading everything about the gains got by reducing pressure I made some changes -It had a Ford Thomson PS running abut 900PSI. I have changed the PS pump to a Saginaw P1 and reduced the pressure with spacers (washers) and have the pump running about 600PSI on oversteer.
While I knew the Pump pressure release only works on OS -I suspected reducing the pressure -was unlikely to be any advantage- with many successes reported and these kits being professionally sold -maybe I am missing something! The higher pressure Ford Thompson actually steers better so I suspect flows are the answer. I think the 5/32 orifice Sag P1 needs to be be re-orificed.
Ideally change the SB but Note a Firm feel SB is very hard and costly to exchange from NZ - which is the obvious answer. Other boxs -I need Left Hand Drive!
I appreciate comments.