It's not just that easy, you stillhave to ream the new guides fr the valves... Thing is, it's not a lot of money for bronze inserts, last seta of SBC heads I had done (abouyt 8 months ago) was 70 bucks. Anyways, I'm not an old fart...just a spry 48, but I've had a few sets knurled in my day, and after about a year of running (roughly 10-15K miles) you could notice a decrease is performance...kinda a "miss", and when the heads were eventually pulled (as alluded to before by an earlier post) the knurkling was about gone, the valves were sloppy in the guides again, 1/2 of the valves had poor facing on them, and couldn't be reground. FWIW...if I was on a shoestring budget, and with the miles posted he'll be running, I'd bolt them on and go...but if I had some spare coin AND since the heads are sitting in my lap, I'd probably take them in and have some inserts put in, and make sure they hard hardened seats...if not, put them in as well on the exhaust seats. The thing is with the good positive Teflon seals as what was posted before, the valve guide boss needs to be machines to fit it, it's not just the same as plopping in an "umbrella" seal. Another thing....what the heck does loose valve guides have to do with a "puff at start up"...when you're alking about umbrella seals, teflaon seals...ect? SUre if the "soon-to-be-brittle-and-break" oring seals provided by GM on the stems go to hell, oil willwick down the valve stems and puff up, but that has nothing to dowith the guides...heck, if you don't beileve me, put a resh motor together, leave them seals out and stand behind it when you fire it up.