Regarding the M-H 12-20's originally painted red here in UK, there is one surviving and now restored tractor in Shropshire where it worked all it's life, the serial number is 103092, I had the remains of another from Cambrdigeshire many years ago, the "U" frame is still in the back of my shed and it was only ever painted red, so far I have not found the serial number stamped in the frame and the plate was long gone.
There is one unstyled original import Pacemaker which has been through three collectors hands and two Cheffins sale's in the last 20 years or so and it has always been painted red, serial number 107343.
Then we know about Dale's unstyled Pacemaker No 107110, discussed earlier in this thread. With regard to the front wheel part numbers you refered to being different on the early ones Dale has confirmed the part number on his flat spoke front wheels is HA 593
Thanks Wayne for the photo of Larry Maasdam's unstyled red Orchard Pacemaker, I have heard of this tractor but never seen it in the flesh yet, I have more to follow soon on the Orchards and Vineyards.