* SM465: This was a heavy-duty 4-speed manual transmission frequently found in K-series trucks.
* T18: Another popular heavy-duty 4-speed manual transmission option.
To know for certain which transmission is in *your* specific 1978 K-10, you'd need to check the vehicle's identification number (VIN) or look at the transmission itself for identification markings. The build sheet (if you can locate it) would also specify the transmission.