Right this has been confusing me as well, so I've been doing some digging.
I've picked some stuff off
http://http://www.rootes-chrysler.co.uk/car-history/spacevan.html and I think it covers the visual differences. I've read it 3 times myself now [|)] but i think it helps
The first prototypes were built at the Commer works in Dunstable in 1959 and tested extensively in Mexico, Spain and Kenya. Series One vans had two, later three, chrome strips between the headlamps and a red Commer badge above that along with a grille for the heater and fresh air inlet. The heater was an optional extra of course – as was the case for most British vehicles at this time!
The Series Two arrived in 1961. The engine grew to 1592cc (from 1494cc) and the grille style was changed to improve cooling capacity. A simple mesh grille was fitted behind the chrome strips.
The Series Two A arrived in mid 1963 had the name Commer was picked out in letters rather than being incorporated into a badge. It also had a new grille, placed just above the bumper. The grille was made up of three chrome strips. The number place moved further up the front panel to a place between the headlamps.
The range was upgraded again in September 1965. All were now available with a three speed Borg Warner automatic transmission and the engine was uprated to the newly announced 1725cc Rootes unit, producing 58 bhp. Diesel buyers also got a new engine – the 1752cc Perkins 4.108 . Externally, the new model could be recognised by a lozenge shaped grille which improved air flow for the larger engines. Proper indicators lamps were fitted below the sidelamps. The range was renamed the PA 1500/2500 series. However, the range had been reduced dramatically to vans, minibuses and chassis cabs. All other body styles now had to be ordered from specialist body builders.
In August 1967, the range was renamed the PB series. Not much else changed apart from the handbrake working on the front wheels and the dynamo being ditchedin favour of an alternator. The range was also offered with a Dodge or Fargo badge in some markets, following the formal take over of Rootes by the American Chrysler company. The Dodge models were known as K 120, K 140 or K 160 depending on payload, the Fargos as F 120, F 140 or F 160.
In 1974, the range was renamed the Spacevan. In August 1976, the name Dodge was adopted across the board by all commercials sold by Chrysler in Britain. A temperature gauge was now standard on the Spacevan along with electric windscreen washers and two speed wipers.
That'll impress them down the pub
