This kind of a hot topic. My experience - milling a head that is warped is asking for trouble. The 4G52/4G54 and G63B heads are forgiving to some extent. You can mill them if they are not too much out of specification but I wouldn't do it as it can affect combustion chamber volumes and mess with tuning (you want all of your compression ratios as close to each other as practical) A good reconditioning shop will check the head, put it through an oven to preheat it, put it through a press to straighten it if it's outside of specification and then give it a light skim to reface it. The 4G64 head is temperamental. They are known to warp so badly that the cams seize up in the cam journals and actually snap in half. It looks like it's the only SOHC Mitsubishi engine that is known to suffer from this failure. But it does illustrate that it's not just the face of the head that twists out of shape if they suffer from a failure - the cam bed also is pulled out of alignment which will cause weird, uneven wear patterns on the cam journals. If your head looks like it can't be repaired, replace it with a non-jet valve head as they are more reliable than the jet valve type. If you're not in a big rush to get your truck back on the road and you are going to use a Weber, tidy up the ports on the head. The Weber likes good flow and is more sensitive to tuning than the Mikuni factory carb. Port matching the intake manifold is worth doing as well. But don't mess with the exhaust ports too much (keep them as close to the original port diameters as possible as opening up the exhaust ports will have a negative effect on performance) The internet is your friend if you are prepared to DIY your own port work. Only basic tools are required (power drill, a flexi-drive and sanding drums plus some small grinding stones - carbide cutting tips and an air die grinder aren't necessary for mild port work)