Well, you'll never get into the 12s with the stock 273 manifold. Maybe with some Magnum or 340 manifolds if you can get them snuck into the early A. Layson's (Spitfire) headers are fenderwell, and I thought that you didn't want to cut your inner fenders. There's a thread on here somewhere about modifying the #1 tube on Hedman's shorty headers for later As so they fit an early A- I'll see if I can dig it up.