Hi Barry;
Sorry for the delay in replying.
The specific float valve for the HIF6 is a viton tipped (resiliant) brass needle without the spring pin. That's what SU supplies. The "integrated" ones you saw would be the grose jet or the ones supplied by Volvo Canada for years. I don't like either of them.
The jets are .100 inch orifice, and there is a white one in the rear carb, and a black one in the front.
Excess fuel pressure can be caused if the phenolic spacer is not in place between the pump body and the block.
The carb that floods is simply the one with the least ability to hold the line pressure - it relieves the other carb and that's why it's normally only one that reveals the over-pressure.
On HS engine vibration can produce a minor flooding condition as the float arm wiggles on the pivot. HIF and the later all plastic HS float are more stable.
The later all plastic float can be used on all HS lids except the very early production ones that used a straight metal float arm. If the arms have the kink in them, that lid can be upgraded to the all plastic float. It's a matter of geometry as the plastic floats are not adjustable (although I adjust them all the time....)
Rhys