'78 MERC 7.5 HP REBUILD

Background:
This is my buddies 7.5 hp Mercury. He couldn't get it started this year and it didn't hardly run last year so I volunteered to help get it going. We had to use all new gas and oil to get it to barely run. Then when running at a higher idle, on decel, it would knock and ping. I suggested we take it apart because it sounded horrendous. I could move the pistons in the cylinder about a 1/16".

So I tore the entire power head apart, which wasn't too hard in my opinion, and found it was a good idea we did so. The pistons are pretty much toast and the rings were surprisingly still there but not doing a lot.

I'm to the point where I need to order new parts. I want to try and find a new set of rings, pistons, and wrist pin needle bearings. Those I can find easily enough on ebay and different parts stores online. But what I'm having a problem finding is a power head gasket kit. Does anyone know where I can find this for reassembly?
Also, any tips, hints, or tricks to reassembly? What kind of rebuild lube should I use for this 2 stroke?

His serial number is 5015859.
Any help is kindly appreciated.
Regards,

https://www.marineengine.com/parts/mercury-outboard-parts/75/4851693-thru-5226934-usa They dont have a complete kit but I think they have what you need just have to order all parts seperatley.

I couldn't find any "sets" but it looks like all the gaskets are available individually. Has your friend considered how much it's going to cost to rebuild this motor and whether it's worth it or not? Just for wrist pin, needle bearing, pistons, and rings he's looking at over $200. By the time you add in all the gaskets an other misc items here and there he's probably looking at $325 + in parts alone. Might be a good time to look for a replacement motor. With what he would save by not rebuilding and what he could get from parting out his old motor, he could probably get close to paying for a newer and possibly bigger motor like maybe a 9.9.