With small caliber scion, best to bark graft.

Tony

I've done double-cleft grafts with small diameter apple (I'm not sure if/how prunus will differ). Two small scions, each one making good contact on one side of the cleft works pretty well.

I have had very good luck with wip grafts with older scion wood. If everything else is good, timing and technique I think you will be fine . Top working strong trees was almost 100%. Small rootstock was slightly less effective with old scion, but very adequate. On a very mature crab apple I actually added fruitwood to and got a couple apples on first years grafts, and a couple more on second year grafts. I have high expectations for the upcoming third year. Some of the pundits on this site called bs, but it happened. Go for it you might gain a year or two on fruiting. Conventional small rootstock will not support fruit, but it can be done for sure. My example may have been more luck than brains, because I did not even know it was fruiting wood until I saw the blossoms, and I was a newbie grafter, but I have learned a lot from this sight since.

I have used 2nd year wood on apples and it was successful. A little harder wood so required more careful work.

Also look into tony's advise. He is one of the most knowledgeable here