Things to take into consideration in my opinion are.....

1: Does it have good compression?
2: Is the carb and muffler on the rear or the side of the engine? (side is better)
3: Is it a long shaft or short shaft? (long is usually better,but its hard to tell till you rip it apart)
4: Do you plan on buying an electronic ignition for it? (I recommend it for a small engine like this)
5: Custom hubs and mufflers are hard for some people to get made or to make themselves,so can you get these made?

Long shaft engines make it ALOT easier to make hubs for,and whether or not your carb and/or muffler is on the side or rear of the engine usually dictates whether or not you'll need "stand-offs". I've found every engine is different,but theres usually a way to make it work if your handy enough or have access to a good metal shop.