86 250 Fourtrax oil filter bolt stripped

My Honda Fourtrax didn't have oil changed for 2 years because it only had about 2-4 hours on it as I only use it to get to the duck blind on flat dirt levy roads 2 mi r/t. When removing the oil filter bolts - all was fine and I put in a new filter but when replaced one of the bolts just spun and wouldn't tighten. I took it out and found out that the treads from the case were on the bolt. I measured the hole and it has more threads inside the case, maybe 1/4 inch. So I figure maybe I can get a longer bolt. This is a 6 sided 8mm bolt head w/about 3/16 in. or more shaft with 11/16 in. of treads under the head. Where do I get a longer bolt and does anyone know mm size to order?
Final question: if this doesn't work can a helicoil be put in? And how do you do that as I have worked on hot rods for years but never did a helicoil job.
Cruise guy