I'm running mustang headers on mine, although they aren't completely in yet, it appears I only have to trim a little bit to make them clear... That's in a fox body however. The mn12 might have clearance issues using them.
They are MAC long tubes and I picked them up for $85 shipped on ebay.
1983 Ford LTD wagon:
351w, Comp cam 280H, Edelbrock Performer intake, Holley 650 DP, BBK longtubes, BBK xpipe, Flowmaster original 40's, 8.8 LSD with 3.73's, Granatelli upper and lower adjustable rear control arms.