I may be wrong but I believe you need
a lift to create the travel needed to use a shock capable of dampening the load created by all that weight coming out of the apple tree.
I would suggest talking to any of the big names in pre runner kits to get professional advice.
I talked with Thuren quite a bit after talking with the larger companies. No b.s straight to the point kinda guy. http://thurenfabrication.com/home.html
Just my 2 cents.