The G63B 2.0 is a belt driven narrow block (designated from the 'Sirius' generation of SOHC 8v) They have a paired port head and the intake/exhaust manifolds are not interchangeable with the 4G54/G54B/G52B engine so keep that in mind. The related 5 speeds are a nut and bolt swap. All Mitsubishi engines have the same carb mounting pattern. That aside, there are kits specifically made to adapt Webers to these intakes. Look up K610 Weber conversion kits - they come with a manifold adapter plate, mounting studs and linkages etc. What I think is the biggest risk of shaving down a 2.6 head is the loss of deck material could seriously weaken the head. The non jet valve heads are more resilient/less prone to cracking inside the combustion chamber but reducing the combustion chamber volume 'may' introduce another issue.

My here are what I think are viable options -

#1 Get the 2.6 head and weld up the combustion chambers and have them reshaped. If you aren't in a rush you can go all in and port + polish the head and sculpt the combustion chambers to remove all sharp edges and improve the air/fuel charge flow across the spark plugs (if you are adding a Weber carb and a set of exhaust headers this will really improve efficiency) Not a cheap route.

#2 shelve the G52B and find a G63B. The G63B is a slightly lighter engine, is forgiving to work on, likes to rev + parts are easier to source (as you've discovered with the G52B head) If you've found a donor truck then chances are it'll also have the 5 speed hanging off it - 2 birds in one bush or... something

#3 full drivetrain swap from a 2.6 truck. Bear in mind that all drivetrain parts are interchangeable between Gen 1 and Gen 2 RWD trucks.

*You can swap the solid front rotors and sliding shim calipers for vented discs and floating calipers from the Gen 2 just by taking the whole steering hub assemblies and unbolting them. Depending on what load capacity your truck has you can swap the front stabiliser bar from a Gen 2 as an upgrade as well.

No matter what engine and trans combo you choose, do the Weber swap. Worth the effort - easier to rebuild, all round improvement in performance (both in economy and HP once you've got it running right)