Yay!!! you got her.What a little beastie.you gonna scrap it?.Awwww.
Jumps on Blumbly's head* Im closer gimmeee the toe ring Lols.
Yeah as Blumbly says the engine is definately a model 5 and by the number id say almost the last ever made.When the sequence run ended they went to letter prefixes with four digit numbers.a,aa,aaa,aaaa,ab,ac,ae and so on,But ive never seen a BB either,so its either really late or an industrial fitment.Anyways its a little beastie regardless,if you dont scrap her,see what correct bits come along in your travels and see how it goes.And remember this is the little mower who gave first life to your Sheerline,by donating her Lung....haha.