Sump Removal

After my efforts with a new clutch and new gearbox, it was made clear that this wasn't the problem at all, however, during the removal of the gearbox and clutch we stumbled across a potential problem, there was alot of play in the crank shaft, allowing the fly wheel to move to and fro with ease, and after abit of research it became clear that this could have been the cause of my motorway problems. A month or so later i removed the sump, for no other reason than to clean it and put in new oil, only to reveal two thrust washers laying at the bottom (This seems to be a common problem with Heralds, if anybody else reading this has had this problem before i'd love some hints and tips as to whether the problem could lay in the size of the thrust washers or perhaps the wear on the main bearings?).

Since this discovery i have bought a new set of main bearings, (6 halves) and am ready to put them in. (i'm also not completely sure as to whether main bearings can be taken out and new ones installed without doing an engine rebuild?)