ariens 10-28 riding mower

purchased my ariens 10-28 mower in 2001.absolutely no issues with it.(just a couple of friction discs). a very nice well constructed machine. i have heard that some of the top end manufactures installed top of the line engines on there machines.mine has a 10 hp briggs powerbuilt flathead engine.(28b707-1142-e1.code is 010405zd. i would like to know if this engine has a cast iron sleeve or just a alluminum bore. (no sleeve). i would like to repower this mower when it becomes necessary.is there any chance of getting a identical engine to the one i have?
thanks for any input.(love this forum)

according to my briggs repair manual it lists the 280000 model series as being aluminum cylinder
the aluminum cylinder versions can be rebuilt (re-ringed, valves, etc.)