Tire chains, size?

20 to 22" cross chains and 110" or so (times 4) of side chain will get you going.

You can put the cross chains every 4 links for good results, or every 2 links for really heavy duty work. The cross chains don't have to be evenly spaced to work well - they just look more professional. They'll bunch up when you start using them.

Cross chains every two links get heavy as the devil to handle.

You can splice the side chains with anything to lengthen or join odd lengths - rod the same size as the chain (or the next size up) works well. There's not a lot of strain on them.

Each side chain will be about 110" long, more or less, depending on the overall length of the cross chains. Longer cross chains will slide further around the tire, making the side chains closer to the center of the wheel, smaller diamerter, therefore shorter. And you will have 4 side chains - two for each wheel. You can lengthen the 8N side chains as required with a splice made in the shop from a piece of rod shaped like a link and welded, using extra chain from wherever.

I'm in Fredericton.

Your 8N cross chains will probably be shorter because of the smaller tire on the 8N. The side chains will have to be lengthened - possibly 12 to 18". You can leave a gap with no cross chains in the extentions, with a bit of loss in traction, but it would be better to add one or two more cross chains.