68 c10 wheels n tires HELP!

[69chevy lwb]

Just start doing some measuring you have a set to work with already if the track width is to narrow deduct back spacing or add wheel width to the same back spacing then measure the diameter of your tires and use an online calculator to find an equivalent in your new wheel size it's pretty straight forward just make notes of what way the tires will move with each change and then check the clearance at full lock and bump