Glyn, will give you a call later when I get chance. It's the 4 bolt rear, on this engine the rockers are in bushes but the bushes have a circlip around them to retain which means the head and bridge has a grove to locate, the early ones with bushes had no retaining groove but held by a "notch" in the bush and a locating hole in the head and bridge and the bolt spacing is different. The later JRM had bearings with half washers at either end to locate and the head and bridge has 2 groves machined in to retain. So I think there are 3 styles of bridge, older one with a location hole, latest with twin groves to hold the bearings in and the one I am after which is the single groove. Gary