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XV Racing and
Firm Feel This is a must read
K Frame weldup My dash is out so I welded up the cowl pinch welds and the steering column Brace. The cowl use to flex pushing on the steering column brace before not so much now. The spot welds holds the car together but lets it flex a lot. Weld up as much you can. Tie the sub frame connectors to the set mounts. A lot of this is low cost with big returns and most will not show. It just takes time to prep and weld.
Good luck as I like the 71 Plymouths as I had a 72 RR/GTX and a 71 RR.