All cool stuff....
"Splayed mains" are a good idea.....The bad part is the original outer bolt holes must be plugged and the plugs sealed in with Red Loctite.

Drilling more holes weakens the main webs even more.
A good girdle on the mainline is not a bad plan...

The brass sleeves between the valves "Was a stop gap BANDAID" to repair cracked heads....

A fresh set of either AMG heads or even the Clearwater heads....NEW IRON that has not seen GAWD knows how many duty (Heat) cycles

Deburing all sharp edges inside the block and a quick hit with a countersink on all bolt hole to remove the stress risers (Just break the sharp edges)

The cooling mods +++
Fan blade and clutch +++
Cleaning up the exhaust ports +++
Intake air cooler + Really works best if the boost pressure is 15 psi or over

Heavy boost on these engines is just a bridge too far.

These engines do not have enough head bolts to really clamp things together well ....Gaskets will not hold for extended mileage

Adding BIG fuel - - -
An IDI (Pre cup engine) keeps way too much heat in the heads where the heat can't be easily dissipated into the cooling system.

A direct injected engine on the other hand (Cummins, Powerstroke or other heavy diesels) have the combustion in a bowl in the top of the piston and the heat dissipates into the cylinder walls and the piston oil spray nozzles get some of it from under the piston head and take it off through the oil cooler...

About 300 flywheel hp on a 6.5 is about it....at least being able to keep the beast alive for a decent amount of miles.

The big power that has been made with the 6.2/6.5 has been for marine use...

Cooling is soooooooooooo easy....You have a huge lake, river or ????? amount of cold water to use to keep the heat down.

Bottom line.

The 6.2 is just not the platform to try and build a buttload of power.

So much could have been done at GM when they hatched these engines.

Deep skirted block with cross bolted main caps (6 bolts)
Forged steel crankshaft
Better head design with more bolts per cylinder
Direct injection (Common rail)

The bean counters got after it...

The 6.2 was a quick fix to get the CAFE numbers across the product line where the company wanted it. And the marketing department sold the public on the idea that these were beasts....Lotsa Torque ......Sort of...

Mission accomplished......
The 6.2.."Little engine that could" got great mileage and most of them lasted a lot of miles.

250K miles was very common..

Most people do not keep a rig long enough for the mfg to justify worrying about much more life span.....

I have seen some mid 80's 6.2 light duty rigs go 300K miles....

Building one of these to do what they were meant to do would be sweet.....As far as making a moose motor......Chasing the wind my friend.....

Much of the "Fixes" for the 6.2/6.5 are/were BANDAIDS to get the rig going again.
Back in the hay day of these engines I have seen many really low mile rigs sitting because people were either not willing to or could not afford to repair them.

This wonderful forum was started to help people (DIYER'S) learn from others, swap ideas and keep their rigs on the road......

Have fun......

What ever you decide to do.....SHARE IT....Always interested in wasssup here at the page...