Cost comparisons
The "333" heads are from truck engine builds, serving both the 348 and the 409 from around 1963 on (I might be off a little on that date). They are plentiful and after Lamar Walden labelled them as "door stops" in a presentation made in 2004, they haven't commanded much in terms of price. In terms of value, they are a good deal for the price. Similar in design, but more expensive are the "817" heads, which came on the detuned 340 horse builds of 1963-65. These will run you more like $750 a pair, as their perceived value is higher. The "1147s" are from the earlier hi performance 348s, circa 1959-60-61. These are also in high demand, even though they don't offer that much more in terms of performance. A good set of these can run you up to $1000. Since they are all about the same, the best value is in getting a good set of the more plentiful 333 heads, match the ports to the intake and gaskets, install some bigger valves and stronger springs to match your cam, and you'll have a pretty inexpensive top end.
You've indicated that you want to develop some power in your build, Used rods are not the place to save dollars. Save them on your heads. Buy new rods and pistons. That's my recommendation, but you can do what ever you want!
Good luck,
TomK