I have used the Earthway chest spreader for larger seed like WR, Oats, Soy beans etc. Holds 40 lbs of seed. Have had mine for ~20 years with no issues.
Earthway Chest Mount Spreader
I've used the Earthway also with very good success. First one lasted 25 years and the only reason I had to buy a new one was because a mouse had chewed holes in the old one because of the seed smell.
So what happened to the "New Neighbor" Thread? Something was off about the whole thing.
I assume Bill nuked it and the poster. Seemed like he was just trolling everyone.
I use a 9" on the conifers & oaks and a 12" on the fruit trees. Note that roots on conifers and oaks will be vertical and fruit trees will be horizontal. Ideal would be 12" as it will handle all.
Here is what I would consider doing, see below. I think your real issue is shading. Very little horizontal light so the tree is really only growing upward. You really do not have much for horizontal scaffolding.
When you prune, you want to prune above a downward facing bud. This will help start...