Muncie M-20 4 Speed Wide Ratio Transmission,
Input: 26 Spline
Output: 27 Spline
Case No. 3925661
Tailshaft No. 3857584
Linkage Plate No: 3884685
Vin No. 14s403350
Date P4m29a

You have some mixed parts in that transmission. The input and case are 1974 model year from a full size or Corvette assembled in St. Louis. The VIN sequence would need to be checked to determine which (Vette or full size). The 27 spline output and 584 extension housing are from an earlier Muncie (70 or earlier). The 74 transmission would have had a 32 spline output and different housing that were about 3/4 inch longer.

That is a true statement.
Nothing wrong with what you have, it's just put together from a mixed bag of parts. It will work just fine with the correct clutch disc and driveshaft yoke.
Thats one of the nice things about Muncies, if something is broke, you very likely can fix it with other Muncie parts. :thumbsup:

Although, I will mention that the tailshaft number is not 3857584. The tailHOUSING number is 3857584 (sorry, we all have out pet peeves).

Although, I will mention that the tailshaft number is not 3857584. The tailHOUSING number is 3857584 (sorry, we all have out pet peeves).

then you mean the tailshaft housing.;)