Nissan/Datsun 720 tire/rim question.

[85 720]

Hello, I just joined the forum. I own a 1985 Nissan 720 4x4 that I sent to Central America a couple years ago. Because I left the manual in the car instead of bringing it back with me, I was wondering, what is the biggest rim/tire combination that I can go with without having to do a lift on this truck. Currently it has 235/70R15 sized tire. I was considering upgrading to a 16 or 18 inch rim but I'm not sure how much I can go without doing a lift. I also do not want to use skinny tires as this is a heavy off roader.

Suggestions are very welcome.

Thanks.