66-73 stock small block heads?????
The 340 cam's specs are readily available on the internets.
The 340s and 360s use larger intake ports- think the exhausts are larger as well. The manifold outlets are larger also. '70s had around 10.5:1 CR, while '71 dropped to ~10.2/10.3. Some early 360s had flat top pistons but I don't know the CR on that.
Where the '68-71 340s were rated to 275, their successor cast crank motors were rated to 240hp. Right around what a stock '92-'02 318 truck motor was rated for. The 360s picked up a little over the last American car 340s and matched that '93-'03 360 truck motor ratings at 250hp. The old motors had larger cams to achieve the power than the newer ones.
The bump in performance in Xs isn't worth the bump in pricetag. Now, for the same price as a set of Xs you can get aftermarket heads that are superior. For the same tag as fixing those Xs up, your aftermarket heads can be ready to run. Unless you have a car they're correct in- you're best off not buying them or selling them and getting something cheaper or better to run on it.
If I had money, I'd build a turbo SBM. A small SBM, with a long stroke.
I think that'd definitely end up pretty wicked with a crude EFI conversion on it.
What I've thought would be real neat for a while now would be picking up a very nice 318 Mag with good bores and stroking it and upgrading to aftermarket replacement heads with big valves and stepping up in the cam department dependent on what it'd actually go into.
