Boas!
Na realidade o AD não fala desse motores XD 88 porque a meu ver estariam relacionados com os Peugeot 403/404/504.
Eis o conteudo de um documento da marca num site de fans desta marca nos EUA:
The earliest diesel/date I can find is the 403 in 1959 with XLD 40hp or XL4D 45hp. They used both these engines in the 204 73-74. The 404 came out in 60 and in 65, a one seater 404 diesel set 40 class records. In 68 the 504 came out, best I can figure by early to mid 70's the XD88 55hp and a couple years later the XD90 59hp. In 78 they came out with the XD2 70hp for their 79 cars. The XD2C 70hp different preheat plugs came out in 80-81. The XD2S 76hp turbo came out in 82. The XD3T 95hp came out in 83 and was still there when they left the USA in 91. The last 504 sedan was 79 and wagon was 84, imported to the USA. The last car was 91.
The only XD88 I saw, I changed preheat plugs in, was mounted in an inboard sailing yacht, in 84. The name "Indénor" come up in my research as a factory, producing diesel engines for commercial use, it was a Peugeot designed, Indénor engine that went into the 403. Citroën was tied into Indénor somehow. Citroën and Peugeot merged in 76, to form PSA Peugeot Citroën.