Transplant 1981 B7100DT engine into 1992 B7100HST?

[Linstrum]

My buddy asked me if it were possible to transplant a 1981 B7100DT (manual shift transmission) engine into a 1992 B7100HST (hydrostatic drive) tractor. The 1992 B7100HST has a dead engine. If it won't be a simple transplant, he won't won't bother with it. He's got about 20 years of experience as an auto mechanic, and I've got around 45 years as a tractor and farm equipment mechanic, so we aren't newbies to this kind of work.