Rim and tire options for my new van 86 G30 4x4
 

Hello, new to the forum, i am having a hard time getting an answer as to what size rims are original and what will fit without altering anything.

at the moment i have 33x12.50r16.5 tires. i want to get a more narrow set for winter use, they are 8 lug, but will 15" rims fit? how about 16"? and i read that there are 8 lug to 5 lug conversion things, do they make them for 8 to 6 lug?
if anyone has been through this already, what would be the cheapest option for tires size?

sorry, i know, a lot of questions out of the gate here. thank you!