67 p10 Stepvan help needed

[Mgicm]

Hi,
So I have this cool little 1967 P10 stepvan shorty and hoped someone could help out with some questions

1. I found that rims are 6 on 5.5 but would wheels from like an older silverado fit? I tried one set and the lugs would not come through the holes. Just didnt seem to sit right. Forgive my ignorance on this but just trying to understand what I should be getting or looking for in terms of backspacing.

2. The van sits so high up with much space above tires to wheel well bottom. How would one lower it without bags and not messing up ride quality (if there is any lol).

3. Does this van have same frame/suspension as same year Chevy vehicle like a pickup?

Thanks!
GP