The zipper ones are somewhat easy to replace.
You just got your truck, right? Do you have a place it can sit for a week or so? Here is what I would suggest. You have no clue what condition the front bearings, seals, u-joints, drive shaft bushings, inner seals, brake wheel cylinders, brake shoes, brake hoses and brake lines are in. Down load all 3 manuals for the M35 from the resource link at the top of the page, read them, study them, buy the hub nut socket from OTC and then put the truck someplace it can stay for a few days.
Pick a side, passenger is easier because you only have the tie rod to deal with, and start pulling the front brakes, hub and knuckle off. Pull everything apart, clean everything up and see what all is wrong. Leave the other side completely together so you can use it as a pattern in case you get stuck and can't figure out how something goes. If you find nothing wrong, great. Order 2 boots from OD Iron, wait a few days for shipping and put it all back together. Then repeat on the other side. Anything you find wrong, order 2 so you can replace it on the other side as well.
If you buy zippered boots, you won't get to inspect as much stuff, learn about your truck or have as long lasting of a boot in the long run.