65 Barracuda Front end Rebuild several questions and a couple of observations

I beleive that undercoating varied with location and also some of it was an option.
My Arizona car had only a thin coat in the fender wells - nothing elsewhere - thankfully.
Look through the sales options at Hamtramck Historical library for '65.

As what to do. Me - I wanted no extra weight and always had hated how regular undercoat eventually flaked and trapped moisture where it did. Others want a car that is really quiet and even install extra sound deadner inside on the floors.

The one thing you want to do is paint any spots of bare sheet metal.

As far as the suspension components go, again matter of personal preference. The lower control arms may never have been painted. Some got a coat of cosmoline or waxy finish. If you're intereseted, do some searches around here and moparts for original finish on component and you find some answers, although maybe not for '65 specifically.
Do not get any paint on the torsion bar hexes.
I think painting the brake drums is somewhat futile, but it was done on some cars.
I've had reasonable success painting the upper control arms (having it last).