I can't testify as to what percentage of 351 swaps are done with a stock k member, but the 351 installed in my car using a stock k member required nothing. It did have a milodon pan instead, but I can't imagine what, if any difference that might have made. The only place clearance could be a issue is at the rear sump. where the dropped rear sump might get too friendly with the rear center portion of the k member. Cutting a small kerf isn't gonna compromise any integrity.