I actually lean more towards agreeing with you guys. Here is the bullets of instructions from mm website
Supplemental Installation Notes
• These instructions are universal for all 1979-04 Mustangs. Steps specific to certain model years will be indicated accordingly.
• All welding must be done with a MIG welder.
• The car’s weight must be on the tires or supported with jack stands positioned on the rear axle housing and k-member.
• Clean all areas to be welded down to the bare metal for the best welding results. This includes the Subframe Connectors if they are powder coated.
• You may find that the floor pan and/or frame rails of your Mustang were bent upwards because of previous improper use of a jack, especially near the rearward mounting bolts for the front seats. If necessary, remove the seat(s) and pound the bent area(s) down, using your foot or a rubber mallet.
• The top surfaces of the bare Subframe Connectors and Seat Braces must be coated with weldable Zinc Primer before welding to prevent rusting. This is not needed if the pieces are powdercoated.
• The Subframe Connectors and chassis frame rails must be coated after welding to prevent rusting.