Making new pedal spindles... those need to be very high quality in terms of steel and heat treat, surface finish on shaft (and does the spindle consitute the loose-ball inner bearing races, or are they cartridge bearings?) as this is a high-fatigue application.
Longer spindles or spacers increases bending stress of spindle and crank, and increases torsional stress of the crank arms. And, things may feel more flexy when hammering the pedals.
Umm... for myself, when I upgraded my crank and wanted a smaller chainring BCD than 130mm, I really had to look to find a "road" crank with low Q-factor, the vast majority were mountain cranks with the arms going further outboard at the pedals; You can't find a high Q-factor crank? Because going further out with the arms is better structurally, the arms are designed to take the load.
A longer bottom bracket spindle would also be sound, that spindle is way larger and stronger than the pedal spindle.