Stan I believe all the OD 883s are the same. They made a iron case version in '75 (I have one) but don't know for sure on other years. They are talked up as being somewhat stronger in the countershaft support area which tends to get oblonged on a well used unit. That can be bushed easily though. If it's in good mechanical shape it will be a nice setup behind that 273. Are you familiar with the ins and outs of the bearing retainer sizes and the bell housing? The OD uses a larger than normal bearing retainer and you need a matching bell housing or one can be reamed to fit very easily by a machine shop. Lots of info in the 4 speed forum on this.