Is that engine new or used ?
The only important thing is crankshaft PTO dimensions as all the other bits will transfer from your mower to the new engine
There are a lot of variations in the basic spec
the drop in Hp should not be a problem
At worst you will have to run a bit slower
I put a 40 series into a 60" JD because I had it on hand on the promise that if it was a problem I would rebuild his original cooked engine for free.
Long story short, we transferred the blower housing and his partner who does the mowing reckons it is running better now than when they first bought it.
Flat 5 acre yard with horses & trailer for shifting hay bales & other horsey things like poo picker yard rake etc etc
