My dad gave his 1965 Model 70. It has a worn out 72 Kohler K161 7hp. Since money is a big factor what type of briggs or one of the "Blue" engins from Harbor freight work. I am not interested in mowing just as a plow horse.
You will be hard pressed to find another engine to replaced the old Kohlers. I would look at rebuilding the K161 that's in it or find an used Kohler. A K161, or a K241 or even a K301 from another older Cub Cadet should work. You will also find, since you want to use this as a work horse, that the newer engines won't have as much torque as that old K161 and won't do as much work either. Another thing to consider is, since the 70 is a narrow frame, there isn't much real estate in the engine compartment. IH mainly put in 7, 10, or 12 hp engines in the narrow frames for this reason (the 147 being the exception).
I hear what yall are saying, however I figure that 15 hp is 15 hp. I hear you guys. If I was a true purist I would do a complete restoration. But alas I'm in a different mind set as I was just thinking of building an adaptor plate and making a puller out of this old iron . However the more I think of it I got an older simplicity for a puller. The only issue with the old 7 hp on this tractor was dad, bored and rebuilt it once already. My brother used it for a while and bored it out again. I am thinking both times were .020 over thats .040 over. How far can I take this out before the cylinders are to weak? I think I will just stay as original as I can with this thing. Any thoughts as to where a fellow can find a good replacement engine if it comes to that? Will post pics as I can.