The base 6.70-15 works out to a 215/75/15 in a modern tire. The optional 6.00-16is a little trickier, as there isn't a direct size match in a modern tire. Closest is a 215/75/16, whcih is just a tad wider and about a 1/4" taller. That size is obsolete, however.
As far as the OE profile, it was closer to a 100% aspect ratio, with the sidewall being about the same hight as the section width. You won't find any modern tires with that aspect ratio.
The OE rims ran from 5.5" to 6.0", which can limit how big you can go. With the 15" rims, I would suggest going with no bigger than a 235/75/15, and then only with the 6" wide rim. That tire has the best availability and selection. Anything bigger will require a wider rim. Fortunatly, 7" and 8" rims are readily available in 6 lug.
