If it's a pre 1968 engine, the engine ID stamped into the front of the RH cylinder head will tell. There might still be a motor mount attached to the timing cover, behind the harmonic damper. If the heads are off, say, for inspection before sale, measure the intake valves. That's what you are really after, anyhow. Big valve C heads.
Toro engine has oil pan with extra capacity, built-in crank scraper, factory windage trays.
The best heads, crank, block, etc. Best-flow C heads, will need hard seats installed for the exhaust valves. Small, inexpensive lifters on the most common bank angle. Big valve E or G heads. Same benefits as above, plus hard seats.