Re: K-27 &/or K-28 Drawing sets.

Responding to your search there are scattered Rio Grande Mechanical Dept K27 component drawings surviving that I'm aware of: drivers, cranks, cylinders and general drawings such as the frame, cistern etc.
Many parts are tabled on DRG drawings because the are common items and the engines themselves were just assembled from stock parts at BLW. Vauclain's 1903 shop book makes no special mention of them on the erecting shop floor.
As has been mentioned Rich Ullin has produced a 2.5" scale version and you might consider purchasing plans from him as a starting point.
The C&TS or Huckleberry RR may have Mechanical Dept drawings. Marty Knox led the rebuilding of 464 and may be able to help you.