028 uses a different pump. 038, 042, 048, and MS380 use the same pump. The worm gear is interchangeable among all of em, (including the 028), as are some of the pump internals such as 'O' rings and such, but the 028 pump body and main pump components are not interchangeable with the other saws.
See attached if ya don't already have em, Pete. Have an 048 project of my own here in a box that I'd like to get to one day. Coupla parts carcasses, too if ya need anything. Also have a complete 042 runner. (Have no idea why in the world they ever made that one.)
And ditto on the good luck.