The 50/50 mixture is a convenient way to mix. I think 58% ethylene glycol (or something close to that) gives the maximum boiling point elevation/freezing point depression. More glycol than that is not a question of waste - it doesn't work as well.

Deionized water and distilled water are not the same (distilled is condensed from vapor, deionized is usually treated), but I think both are completely fine for cooling systems.

the "extra" holes in your running board are to mount the full length trim of a 1903.

with all respect to the owner of the 36, I think "all original" means "unmodified" instead of "unrestored"

I think either the original Clipper convertible or its recreation was peach

My 49 has a glass tube mercury switch, but I cannot say I am sure it is original

TriPlex laminated glass technology (a sandwich of glass and butyrate) came from Pilkington. The Triplex name and xXx mark was used for a long time (1980's at least)in Britain. Pilkington now owns L-O-F (Libbey-Owens-Ford) glass and still produces auto glass.

how is the starter engaged now? The original had a button under the gas pedal which disengaged on engine vacuum, I believe

Can you share how you intend to adjust the seals? I have the same problem with an aftermarket trunk seal.

The pre war AC cars used a quilted insulation on the roof - LeBaron Bonney's is a good replacement. I got the single sided foil to make sure of a good bond, and used a recommended 3M adhesive as instructed

burning a gallon of ethanol releases less energy than burning a gallon of gasoline - that's the thermodynamics, it has nothing to do with the design of the engine.