What I meant was, do you know the oversize? Standard bore size is as you say, or 3.375", then you have rebore sizes, which on a Bedford, are +.005", +.010", +015", +.020", +.030", +.040", +.050" and +.060". When you got to the limit, liners could be fitted and you start from Standard size all over again. If you carefully clean the top of a piston, one of these oversizes should come up, stamped on it, or STD, if standard. After all these years, it has probably been bored a few times. You will need to know this size before ordering rings.