That's not a 4B series engine, it has similarites to the 4B series but the throttled air intake is a major departure.

In NZ we had Isuzu trucks in the early 80's which were badged "Isuzu-Bedford", we're talking pre-runner to the NPR series of around 1985.
A neighbour had one which had a 3.9 litre engine with a lower output than the 3.3L 4BC2 which came in the first NPR's.

The truck model may have been a K20 or something similar. The Isuzu parts dealer had a wall poster showing the trucks from way back then, but I have moved and can't refer to it.

Regardless, if that rocker cover will fit my 4BD1T then I want one. <img src="/forums/images/graemlins/smile.gif" alt="" />