I have various F series powered mowers. Other then possibly different carburetors, how does one determine which one has 3 1/2hp or 4hp or 5hp? Are all the blocks and pistons the same? Can I take the Walbro carb off my 5hp 680553, install that carb on my 3 1/2hp 6280 and have a 5hp 6280? Thx.