A spring over conversion isn't really that hard to do. The devil is in the details. You basically only have to weld spring perches on the top of the axle tubes and then bolt the axles back on. Some of the issues that you'll probably run into are:
Setting the proper pinion angle on the rear axle. This will be determined by what type of rear driveshaft that you will be using. A double u-joint type shaft has a maximum operating angle of about 15°. If you raise a CJ5 very far you'll quickly go over this limit and so you'll have to go with a CV type rear shaft. This means that the driveshaft and pinion will be almost in line. You need to set this up before welding on the spring perches.
While were on the subject of the rear axle, one of the negative effects of a SOA conversion is axle wrap. You need to determine how you will deal with that.
The big problem with the front axle is the steering. Springs on top of the axle often try to occupy the same space as your tie rod or drag link with less than desirable results.
Going with high steering is one way to deal with this problem but a pricey one. Also be sure that your caster angle is correct before you weld the spring perches onto the axle.
You may have to deal with shock mounts, brake lines, lengthing the front driveshaft and things like that. I would make sure that the $450 kit addressed these issues.