If you can mount them vertically, terrific. If not, as was stated, closer to vertical is better. Specifically, the net effectiveness of the shock/spring rate is found by multiplying by the cosine of the installed angle, relative to 0 degrees as vertical. For instance, if your shocks are mounted 30 degrees off vertical, the effective ratio is about 86% or so. Since the cosine function is non-linear, the more the angle, the faster the rate will change. Above 25 degrees or so, things start to drop pretty quickly.
This is important in terms of the dynamics of the setup. If your ride height/static angle is at some angle, use 30 degrees as an example, but increases in bump quickly, your setup will effectively become a falling rate setup in bump, which is generally not desireable. For instance, if the angle drops from 30 degrees (static) down to 45 degrees in bump (not an uncommon amount for several systems I have seen), that represents a big change in effective rate. Suppose you have a 250 lb-in spring, at static the effective rate in this example is 217 lb-in. The same setup at the example 45 degree bump results in a 177 lb-in rate, and that is a heck of a drop in rate.
There are several, several OEM configurations that angle the shocks quite a bit, such as early Mustangs and Novas, and there are a lot of aftermarket setups that do the same, mainly as a packaging compromise. I giggle when I hear the aftermarkets guys saying they did this for performance reasons, completely opposite of reality. If you are building your own setup from scratch, you usually have the luxury of establishing the mounting locations, etc, but most often you are restricited by "immovable" things otherwise, also known as frame rails!
By the way, you picked a darned fine setup to model your rear setup off of.
Mark
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
Coil Over Mounting
Linear Mode
