[Super73]

That looks like the stock location for the shortbed as well. I notice you made the front mounting point adjustable, good idea.

Springs appear to be furtner back towards the axle than on a shortbed. That will put less leverage on the spring, meaning you can run a lighter spring rate than a similar weighted truck with stock location. There are pros and cons for this.

My guess on why you are not getting much tire spin at the track would be directly related to gearing and converter. You have a TH400 which has a 2.48 fist gear and a 3.08 rear gear with a 32" tire. Not sure about verter. That combo's means you have an amazingly lazy first gear and you are not hitting the tires very hard at all.

For comparison sake:
TH400 + 3.08 + 32" + 6,000 in first = 71mph
TH350 + 2.73 + 35" + 6,000 in first = 71mph
Powerglide + 3.73 + 28" + 6,000 in first = 72mph