Best for articulation is how AaronB has his. Best for street, would be almost vertical.
I also would go with a 12" shock, and if it sees a lot of DD duty, run them like this / \ not as drastic an angle as Aarons, space out the top mounts mabye 6 inches or so. That'll give you more use out of the shock, but still allow decent articulation off road.
I think what I'll do is before I welt in the upper cross brace(upper shock mount) i will drill a serries of mounting holes. from dead center out 1" and every inch up to 4".. which will give me 5 different possitions to mount the upper portion of the shocks..
also BLACKDOG do you knowhow much up travel the the rear 4" marlin leafs are suppose to travel (w/ 6" shackles)?? I haven't set the bump stops in yet to the U bolt plate. I want the bump stops to limit the up travel not the shocks