Hi Baza
I am the biggest fan of the real last big Opel, called K (Kapitaen), A (Admiral) and D (Diplomat). There where two series.
The A series was build between 1963 and 1969. Kapitaen, Admiral and Diplomat had the same bodys, but differences in detail. 1963-65 standard engine for Kapitaen and Admiral was the 2.6 OHV engine (100 PS). The Diplomat was fired by the V283 Chevrolet V8 engine (4.6L / 190 PS). The V8 engine was optional on Kapitaen and Admiral.
1965 was an update. The 2.6L OHV engine was replaced by the 2,8L CIH engine. 125 PS with single carburetor, 145 PS with double carburetor (2.8 SH). For the Diplomat the 5.4L V8 engine was optional.
Also a Diplomat A Coupe was launched, build by Karmann in Osnabrueck. Very, very rare today and only available with the 5.4L V8 engine. 2 Prototypes of the Diplomat A Coupe are converted to Cabriolets. One of them still exists.
1969 the B series came up. It was a revolution in wheel suspension and brake systems. The KAD B series used the most expensive rear wheel suspension: De Dion.
Brakes: Ventilated disk brake round around on the V8 and 2.8 E models . 1969!!!
The 5.4L V8 engine (230 PS) was only used on the Diplomat B V8. All other members of the series had 2.8L straight six CIH engines, carburetor / injection 132 PS...160 PS.
The 2.8L straight six was later converted into the 3.0L used in Senator/ Monza A/ Omega A. Top of the line was the 3.0/ 24V, based on this old engine with a 4 valve head, used in Senator B and Omega A. Lotus in UK set the i point, the 3.6L Biturbo. The worldwide fastest limousine at its time. (Lotus Omega)
Rolf