There appears to be transferred aluminum form the piston on the intake side, but it's hard to tell from a picture. If there is, replace it or replate it. If not, make 3 quick passes with a 4" bottle brush hone (280 grit, aluminum oxide or softer). If that eliminates the visible scratches and "shadows" from the top ring at the top of the bore, then the cylinder is usable IF
the clearance to a new piston is correct and iy measures straight/round within tolerance.
The valves should be tested for leaks before disassembling by filling the ports with solvent. Seepage is tolerable, but more than that and a valve job is in order. Eveb if the valves pass a leak test, they should be inspected for wear. DO NOT
mix them up if you intend to reuse them; make sure you know which port they came from. Here's a guide to what you're looking for:Valve wear
Anything that looks more worn than the one at the upper left should be replaced. Replacing valves REQUIRES
the seats to be refinished, and this is a job fro a professional machinist with specialized equipment. NEVER
lap a titanium valve.
With a 426, you have the option of using the stainless steel valves from the 2000 model, which cost about a quarter of what the Ti valves do. Be sure you also buy the correct springs for the 2000 valves.