Correct TR4A Oil Pressure; IRS rear end ; Handling

As the weather has finally improved, I took my recently acquired 1966 TR4A IRS for its first longish drive, mostly in Chicago suburbs so a fair number of lights but mostly cruising at 50-60 mph. The oil pressure starts at cold idle around 50-55 than ran in 60-70 range. At the end of the drive, the running pressure was down to about 40. I started the car later in the day, and got the same cold readings as before (and as usual). I don't know what oil grade is in the engine, as I have not changed the oil since I got the car (with fresh oil) a couple of months ago. This all seems normal, but would be interested in other views.

The next question has to do with the rear suspension (which has a tube shock conversion). The car seems to settle very slightly at the back (maybe 1/2" at most) when not driven for a while, but after a drive seems to be quite level. I have seen some very saggy IRS cars and have read of issues, so am interested in views on whether to be concerned or what to look for. Weakening springs maybe; shock adjustment? I sometimes hear some quiet clunks (which seem to come from the left side) when moving out in first gear, which I gather are common (u-joints, but maybe splines or diff mounts?), but again would value some perspective on what to look for. I also found that the previous owner installed twist-in spring boosters in the front, presumably raising the front a half inch or so. Sign of weak springs?

Finally, I notice that the car seems to tend toward oversteer, and note rear tire squealing on tight lower (25-30 mph) speed turns. I once had a live axle TR4A which handled neutrally but less familiar with typical IRS handling. The tires are roughly half-worn Dunlop 165-15 radials (on 72 spoke wires) inflated to factory pressures. There is a definite wear pattern on the inside tread, maybe indicating too much camber?

Thanks in advance for any thoughts!

Lynn White