well the older 25" mowers came with the B&S 8hpThis is a 223cc engine with 10ft lbs of torque. Would make a monster push mower engine.
Snapper RER's in 28" normally are 10hp, 30" say 12'ish and the big 33" deck is 14.5hp-16 ish. My 33" Snapper has a 14.5hp 400 something cc Briggs.
The pic below, that engine doesn't belong on a RER.
the 28" had the B&S 10hp and the 30" often had the kohler 13.5hp
on the newer mowers now they are almost exclusively 28" with B&S 11.5hp and i have two of the 33" and one has the B&S 12.5hp and the other has the B&S 11.5hp
i was thinking too that its not right so i double checked everything and its the original motor for that mower according to the model numbers and it comes with a special mounting plate for that motor to foit it so its not jery rigged its oem. a 28" isnt that different then a push mower and its direct drive off of axle so while it seems small it has no issues doing its job