71 and later gm heads had the hardened exhaust valve springs installed at the factory.......and if they are not cracked,build em up, why spend more than you need to . great if ya can drop betwen 600-1000 on a pair of aftermarket heads, mind you some are very wicked. but in the long run if a set of small chamber heads can be had for cheap then go that route...i have couple paires of old gm iron heads in my shop.....back in the 70's they were bolted on the 370hp LT-1...cant all be that bad.