4 bar set up questions

[69charged]

hello all. i am about to order the morrison 4 bar set up but have a few questions concerning the set up/fitment. i have to weld in a crossmember to the stock frame rail for the front bar mounting brackets but where? in terms of height from the ground. i will center the axle in the wheel wells then fit it up but does it matter if the bars are level at ride height or not? i am very new to this so give me the explanations in low mans terms!!! also is there a certain distance apart for the bars that is better? i would assume that wider would be better but you all know what assume is!!
any help would be great. going in a 69 charger

thanks
clarence