I think the oil filter compatible blocks were these fitted with timing chain. Even then, there was no filter fitted at the factory, but there was provision in case of a future engine rebuild using bearings other than the original white metal type.
Gerrie, on the position Malcolm described you should see a round cap fixed with a hexagon bolt (19mm?). This is to be removed and a filter fitted instead, provided a threaded pipe is fitted on the bolt position. They used to be obtainable, but now they are hard to find. It's very easy to make at a machinist shop, though, if you show him the bolt to determine the correct thread.