I've also been informed that the engine now in the bike is a later version that the one used to win the '74 title. We'll see what unfolds.
last year Pattern ran a 75 MXb motor, i know i picked it up when we were on the start line and told him so ( ok and maybe 211 as well)
Sorry 52 but im prity sure more than the numbers change on a 75 model, its basically a 76 YZC, try fitting the side covers onto the 73/74 cases ? the barrel and heads dont even look similar, never mind some of the internals wont interchange even if you could replace the whole guts and make some changes.
From what i remember it was a 75 motor they had fully rebuild and its not the one his dad had, that was at home broken somewhere, its 'like the one his dad had' he said to me, thats two differant things and 30 years is a long time between what they looked like.
ITs a major component but if you like we can run a stack of 75 MX 250B' in pre 75 and put a solid bar in the mono shock place to match it up