Sounds like you need to replace the piston squirters. It's the only way to be sure you're in the clear. Your assumption is correct that the faulty squirters (the ones not squirting oil well) will lead to increased piston temperature. Not sure about detonation but seems plausible if head temps were way high.

The other solution I know of for cooling the pistons is notched sides of the rod.

https://www.youtube.com/watch?v=7wuNuuEoN7Y

But i'd just replace the squirters and be done with it. It's not terribly hard to do. Just takes patience.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/906368-piston-squirters.html

The rebuildable squirters by Catorce/Taormina are a decent value when you consider the cost of the original Porsche squirters. Plus you can actually clean them, which is a really nice feature.

I've heard of some putting an always-on squirter in place of the check valve type. Apparently it's quite simple by using a set screw (hex "in-head" like a socket head screw) with an appropriately sized hole drilled through. The squirter passage in the engine case is therefore tapped with threads to accept the set screw and loctite is used to secure it. Mike Bruns (MBruns) here on the forum could elaborate more if necessary, as I understand he occasionally used this method when he ran the engine shop at JB Racing.

That picture of the cylinder wall looks like a casting defect. Nothing wrong with boring the 95mm cylinders to 98mm and re-plating. You have the best cylinders for doing this since they are the Carrera style with the groove-less sealing surface on top. The earlier SC cylinders use a sealing ring and boring them to 98mm makes for a very thin area between the ring groove and the ID of the cylinder.

Get the pistons of your choice (staying with single plug ignition, you'll want the wedge style "Max Moritz" piston shape and both CP or JE make that shape) and send one with the cylinders to US Chrome for boring and re-plating. All you need to specify is the required piston clearance.

Chip mapping is pretty straightforward as a lot of people have done this. So the basic re- map has been figured out by the chip providers. After you get it running and broken in you can fine tune the map further with a qualified tuner on the dyno.