Tire finding trouble please help

The other issue when replacing the older car tires is the tubes. Anything newer does not do well with tubes internally unless they are designed to work with tubes.
I had a friend from a tire shop who would put half a container of baby powder in each one to help lubricate the tubes and allow them to last a bit longer.

Will your older rims would tubeless?
The car currently has tires on it that are biased ply and have tubes in them. They are 6.50 x 16 and from Montgomery Ward. I had one tire place tell me that the DOT wouldn’t allow them to put tubes in tires anymore. I have plenty of room to put larger rims and tires on the front wheels but the rear wheels don’t have a lot of space so I’m trying to stick to original size. It’s literally driving me nuts I spend too much of my spare time looking for answers. I called tire rack And they can’t help me at all. I’ve been to Discount tire and they keep telling me I can put larger rims and tires on the car because there’s room but then they tell me I need to drive the car there to make sure I know this car better than they do . . .