I would suggest the kit no matter how many miles are on your car... makes the install easier, and besides, you'll need all new shims anyways.
*01 Cobra, 4.6L, P&P heads, Stage 3 comp cams, MAC LT headers, O/R Hpipe, Bassani catback exhaust, Too many bolt-ons to list..., 4.30 gears. (364 rwhp/ 330 rwtq)
*01 Roush Stage 2, 4.6L, 5 spd, BBK Bolt-ons (Wife's)
*71 Chevelle, 350, 4 spd, H/C/I, (~400 hp)
*72 C10, 350, Auto, (my Daily Driver)