Why not build individual planters? I do mine out of redwood; approx. 13 inches square and about 13 inches tall.
Advantages of planting boxes: portablility, control of potting medium, great displays possible.
Disadvantages: wood of planter degrades, size of plant might be less than one planted out.
It's up to you, but these things look great in planter boxes or containers.
FYI: my soil is somewhat clay here in Northern CA. My JMs planted out in it do great. Depends how nasty your clay is.

Well, the idea was to save money and later extend the raised bed and build a retaining wall of rock around it. I also wanted to hurry and get them in the ground because our yard was bare in the back. We just bought a house and I have 13 jm's I have been scrambling to get potted,repotted and planted, lol.

Follow your dream.
JMs are shallow rooted so a raised bed would enable you to have a nice medium over the clay.
Only 13?
I have 15 in individual planter boxes. 7 more in one-gallons. I have the wood to build more planter boxes and now that the weather is fine...just one more project to get started on. Like I need another project!

Yea, always seems to be another project with gardening. 13 JMs is just my cutoff for the spring or the wife might flay my hide off. She needs new furniture and I am addicted to JM's, not a good mix.