Yes you can do that.
225 70R15
That's a much smaller tire, you may want to think very carefully about that. I certainly would not.
that is fine, check for rubbing under wheel well.
Most full size cars of that era used P225/75R15-size tires Please note: The tires on my 1969 Buick Electra 225 are 205/70R15 and they are on the factory rims that came with the car.
Maybe, if enough clearance on full steering lock.
If there is enough clearance for the wider tire, yes.
Usually this is written on a sticker on the driver's side door, however sometimes this gets painted over so is not visible. If it's a standard 15" wheel, the most common one for this pickup would be 205/75R15, 215/70R15, 215/75R15, 225/70R15, 225/75R15... all these will work, they may just be an inch narrower/longer or slightly slimmer/wider, but will still fit the same wheel. Do a search on "tire calculator" and you can put the size of your current tires and then compare them to some of the sizes listed here and it will tell you exactly the difference in measure against your new tires.
You can but know that the 75 tire is going to be slightly taller than the 70 and because of that will have a slight effect on your speedometers accuracy. The 75 or 70 is actually a percentage figure telling you the tire sidewall is 70 percent as high as the tire is wide.
205 70R15
P205/70R15
215/70R15
215/70r15