help with my new MF10

Howdy, just picked up a new to me mf10. I'm not sure of the year, I havent had a chance to look into everything. I have a few ID questions, as it looks like it doesn't have the original motor. Can anyone tell from the pics which craftsman motor that is, and what horsepower it would be?

Also, the shifter has the first hear location blocked off. I'm not sure if that means 1st gear is busted, or it is perhaps a different trans that is only a 3 speed.

Other than those two things (non original motor, and transmission quandry), it looks like it is in great shape, and runs great! The 42" mower deck works flawlessly. It looks like someone put in a lot of work to restore this. The guy I bought it from got it in a trade, so he really didnt know much about it. I almost passed due to the unknowns, but it looks great and runs great.only thing it could use is a shifter adjustment for 2nd(1st?) gear, as it is a little hard to find

Any info based on the pics as to what I've got would be helpful. Or if you know where I should look for ID markers.

Thanks!