Pr2501,
Don't be distracted by the 307...308etc.designtaion(it is more or less the 200D...or 250D badges on a w124 for example). IMHO it`s the chassis type that matters. So,your van is a 602...This chassis family was equipped with om616,om617,om601,om602 and some gasoline engines like M102 and M115.

I think the authorities are quite familiar with those details.

Here you are:
Technical data for Mercedes 602 Van / Flatbed

Edit:
...can legally drive only with motors which were used on that campervan for that year...
Wow,that narrows it...are you sure?
Acc. to EPC, WDB602.367XXXXXXXX were fitted with om601 too...for the Japanese market...but from which year? Or produced along with the other?