Did the L29 heads bolt right up to your older 454 or did you have to make modifications? Did you see good performance gains with these heads? Thanks.
They bolt right up. You will want to remove the valve spring rotators and replace with solid shims--16 pieces required. There are at least two part numbers for the shims depending on what valve springs you want. Watch the intake valve guides as the machining is not perfect and some spring shims will not clear the poor guide-to-spring pocket fillet without some help from a die grinder.
You will want to remove the rocker studs and either machine the heads for "normal" BBC rocker studs, or purchase the "conversion" studs that screw directly into the net-lash heads. Similarly, you'll want adjustable rocker arms/hardware.
Oversize valves probably won't flow any better than the stock ones due to valve shrouding issues.
The intake port has a ski-jump cast-in to induce swirl. Not the best for performance.
The castings have 7/16 accessory holes; some other castings and accessory brackets use 3/8. I had to sink a drill bit through the brackets bolted to the heads and switch to the larger bolts.
Overall, there's a ton of information on these heads on this web site, use the search function
and you'll find porting info and lots of other stuff.