Hi Chris,
I contacted miller and they confirmed that their semi synthetic is a low detergent oil like their mineral classic 2050, and that it's suitable for the v8.
They gave the following report based on my car too - tells you their oils that match specs.
P6, 3500, 1968-1969
Manufacturer:
Drive type: r.w.d.
Cylinder capacity: 3531 cc
Power output: 160 HP / 118 kW at 5000 RPM
Engine
Petrol, 4-stroke, 8 cilinder, V, 2 valves/cyl, liquid cooled
Cylinder capacity: 3531 cc
Power output: 160 HP/118 kW at 5000 RPM
Capacity 5.7 liter
Filter capacity: 0.6 liter
Use: Normal
Check 1000 km
Change 8000 km/6 months
OEM recommendation
temperate climate API: MS SAE 10W-30
temperate climate API: MS SAE 10W-40
temperate climate API: MS SAE 20W-20
Company products
temperate climate Classic Performance 20/50
temperate climate Classic Sport 20/50
Transmission, automatic
Automatic
Capacity 8 liter
Gears forward: 3
Gears reverse: 1
Use: Normal
Check 8000 km
OEM recommendation
year-round ATF, Type A Suffix A -
Company products
year-round Millermatic ATF UN
Differential, rear
Capacity 1.25 liter
Use: Normal
Check 8000 km
Change 32000 km
OEM recommendation
temperate climate API: GL-5 SAE 90
Company products
temperate climate Hypoid 90 GL5
temperate climate Hypoid 80w90 GL5
Hydraulic brake system
Use: Normal
Check 8000 km
Change 64000 km/36 months
OEM recommendation
year-round SAE J1703 -
Company products
year-round Universal DOT 4 Brake Fluid
Grease points/nipples, wheel bearings, front
Use: Normal
Check 16000 km
OEM recommendation
year-round Lithium base multipurpose grease NLGI No. 2
Company products
year-round Delta 2EP
Grease points, 'de Dion' tube
Use: Normal
Check 16000 km
OEM recommendation
temperate climate API: MS SAE 10W-30
temperate climate API: MS SAE 10W-40
temperate climate API: MS SAE 20W-20
Company products
temperate climate Classic Performance 20/50
temperate climate Classic Sport 20/50
Cooling system
Capacity 8.7 liter
Use: Normal
OEM recommendation
year-round Water with antifreeze (ethylene glycol base) -
Company products
No product found
Carburettor damper
Use: Normal
Check 16000 km
OEM recommendation
temperate climate Heavy Duty Motor Oil (classics) SAE 20W
Company products
No product found
Steering box
Use: Normal
Check 16000 km
OEM recommendation
temperate climate API: GL-5 SAE 90
Company products
temperate climate Hypoid 90 GL5
temperate climate Hypoid 80w90 GL5
Hope that's some help to somebody else
Rich