Hello
Surf61 and Welcome!
Here is a thread discussing that question. Looks like you can do it.
http://www.67-72chevytrucs.com/vboard/showthread.php?t=428936&highlight=yokohama
I used to have 235x70x16"s using wheel spacers. I had 215x75x15's put on the original 15x5 rims, but found them too short. I used to have 3" lowering rear springs, but found they were not designed for the heavier suburban rear so I had air shocks in the back.
I returned to 1.5" lowering blocks and the stock springs and am happy with the look and the tall, skinny Yokohama tire referenced in the link.