It would be helpful to have your engine serial number Mercury Outboards part system works off of serial number groups not years. My experience has been that many times people think there outboard is a certain year and they are incorrect. That being said, on the CDI website they list two different stators for the 70hp Mercury you list in your post a 9 amp and a 16 amp stator. If you originally stator had 398-8778A16 or 398-8778A10 stamped on it then it is a 9 amp stator. If you originally stator had 398-9710A12 or 398-9710A14 stamped on it then it is a 16 amp stator. Your exact engine serial number will also help identify if you have a 9 or 16 amp stator.
If your engine originally had the 16 amp system on it then it should already have a voltage regulator. Use the web page below to help identify what you have reference number 42 is the 9 amp rectifier and reference number 43 and 44 are the 16 amp rectifier and regulator.
http://www.marineengine.com/parts/m...40451-thru-0c221999-usa/electrical-components
marineengine .com/parts/mercury-outboard-parts/70-3-cyl/0b240451-thru-0c221999-usa/electrical-components
It is possible to overcharge your battery and damage electronics with the 16 amp stator that is why CDI recommends using a rectifier regulator if you do not already have regulated system already. I am not aware of a plug and play kit you could install to convert your straight 9 amp rectifier only system to a 16 amp rectifier regulator system. You kind of end up on your own when you start modifying your outboard from its original factor design. Call CDI and see if they offer a kit and see what rectifier regulator they recommend you use since your setup will be different from the original factory design. If CDI does not have a kit you're going to have to do a little rewiring on your own to install a rectifier regulator in place of a straight rectifier only setup.
If you have the 9 amp system already and do not want to modify anything then use CDI part number 174-8778K 1 that is the 9 amp stator recommended for the outboard you list.
If you modify your outboard and use the rectifier regulator CDI part number 194-5279 you list make sure the at least one of the attaching bolts has a good ground connection or run a wire from one of the attaching bolts to a good negative ground. The yellow wires of the rectifier regulator attach to the yellow wires that come from the stator. The red wires attach to the other red positive wires on your outboard they can connect to the same connection point. The gray wire is the tachometer lead and you should have a gray wire in the main engine harness that would go to a tachometer assuming your engine has a tachometer. If you do not have a tachometer the wire can be left unused just tape it up so it cannot short out. I hope this info is helpful.
