Greetings,
Mr. M. Not trying to be glib but with enough $$ almost anything can replace the Lehman with consideration of the comments made by Mr. kc. I re-read some of your older posts and saw you were considering Volvos. Did that not materialize?
I suspect with original 120's in a 44' boat you were probably overpowered. Perhaps replacement motors in the 80HP range would be better suited. Of course it all depends on availability and $$. In any case, whichever engines you eventually choose will require alterations to hosing, mounts and probably electrical among others.
We have twin Lehmans (hardly broken in @ 4000 hours) and I've pondered about replacement if ever necessary and, although I have little idea of the cost and complexity, I would seriously consider replacing the twins with a single mounted amidships. Keep the twin props and run either hydraulic or chain drives to the individual transmissions. Ah, pipe dreams...