Agree with Pat....those heads are not a familiar casting num. to me, and I have been around GM big block heads for awhile. Mortec doesnt list the runner size on them, so I would be concerned about that part. You can put the larger valves in them, but if the intake runner size is small (peanut port heads), that won't do any good. Are they the heads that came on the block originally? If so, you might as well forget about using them, they wouldn't put anything but a small runner head on a truck engine. They would be great for lower RPM, and have great torque...you would smoke the tires for miles with that engine...but you wouldnt have any top end. So if you want to use those heads, I wouldnt even do the larger valves, it wouldnt do any good. If you want to stick with GM heads, (good idea by the way) look for a set of 781's...they make a great performance head...put in the larger valves, have some mild port work done, and you'll be good to go. They were very common on 454's throughout the 70's, and there are lots around...049's are basically the same casting, but they only used them one year, so not as many around. On the hardened seats, if you would be more comfortable with them, go for it...but it's not really a 'beat on it' issue, it's durability, so with the amount of driving you'll be doing, I still dont think they're necessary...but that's up to you. I have had my Chevelle with non-hardened seats on the road since '98. I drive it several times a week during the nice months, run on 91 or 93 octane. I run it very hard quite often. I pulled the heads for a new engine that I built 2 years ago, and had them freshened up while they were off. The machine shop said there was no indication of any seat deterioration due to the no lead factor. But like I said, if you would feel better doing them, go for it for peace of mind. What are you doing for pistons and rods, compression ratio, etc? Good luck with your build, and keep us posted. John