Torsion bars or after market front suspension? I have run low deck sr heads to -1's with tti 2 inch headers and torsion bars manual steering box. When I went to the 572-13's I bought a alterkation front suspension and went with the 2 to 2 1/8 step headers. With the aluminum block I had to sink the side main cap bolts in and a few other small mods to get them to fit. The Pittman arm on the torsion bar setup also rubbed and I clearance it too.