As far as running Reg. Unleaded in an older coleman lantern or stove.... I have been doing this for a while now in my 1968 model 425D stove and older lanterns and they work great... I do add about 1oz. of automotive fuel injector/carb. cleaner per gal. I have never had a problem yet. I have used about at least 6+gals threw this stove in the last 3 years.... I think what also may be helping this is that all the unleaded gas these days has at least 10% ethenal in it there fore burning cleaner. Also remember to only use the 87 octain or less not more.
I am curious about the Naptha..... where are you finding this and is it cheaper or the same cost as 87 gasoline?