Hi Anthony
You didn't say if the motor you've been offered is a rear or side exhaust. If rear exhaust you will need to use a 180deg header. These are good little motors and yes they are stronger than the K&B. If you want to they can be modded up but they go pretty well standard. These were some of the first Piccos that Ron Paris started playing with.
I'd have to be honest and say they are not in the same league as a NR, Mac or modded CMB but it depends on what you intend to use it for. They are a good solid motor but don't have the high HP of the later LS designs. If it was at a good price it would make a good toe in the water 21 and will thrash a stock K&B.
GT