318 Engine stumble

That's a nice starter curve. I like the kink for 87gas.I wouldn't touch it for now. I would set the maximum to between 32 to 34, and let the idle be what it will be. Personally, I'd like to see that kink up a lil higher, at say 2800. But if the power runs are clean with no detonation, then let it be.

Then I would put the biggest Vcan on there I could find, or mod the one you got, in either case crank it up to about 22*. Then adjust the screw inside it to bring it in as fast as possible .
Now look on your graph, and add 22* to every point on it.
That will be the grand total available at Part Throttle.
Notice that at ~1800 this will be 22+25=47, Perhaps a tad high, we'll see.
Then, look at ~2400; and I see 22+31=53*, Perfect for cruising with 2.94s;
And finally at ~2800, and I see 22+32=54*, Perfect for cruising with 3.55s.

Do not confuse piston slap at low coolant temps, for detonation after fully warmed up. I have never heard detonation at idle. If you have piston slap, you just gotta ask why it's there. Did you build it into there on purpose, or?

IDK which 600Holley you have but Holleys are not known for their stellar fuel-economy. A better choice is something with triple boosters and metering rods. Even if it's a big TQ or Q-jet, or just about any spreadbore..... installed on a spreadbore intake. I wouldn't mess with adapters. I have a smallport, cast-iron, spreadbore intake, so I know they are out there. Your combo might be perfect for an Offy Dual-Port. I recently acquired one of these, but haven't had a chance to experiment with it yet. At your stated useage,with no WOT running, consider a 2bbl carb.
OK I see your 4-corner 600. The problem with that carb is that it isn't really engineered for economy, adjusting the low-speed circuits is not easy. Whereas the TQ and QJs are; they have multiple ways to adjust just about anything as regards the lowspeed circuits. If you don't need or want the secondaries, then you can simply block them closed. If you do that with the TQ, then get the bigger-rated TQ; it has slightly larger primaries.
But honestly, The TQ runs super- great on a smogger-teen. I have one on my winter motor. The 850 no less. The engine will never pull more than it can pull, so if that happens to be 200 or 250 cfm, well that's all the 850 will pass. But the 1.5" primaries (on the big one), have almost instant throttle response, so if you can make a TQ bog on a smogger-teen, then it must be your first tune,lol.
But hey, I also gotta tell you that the Holley 600 can make 32mpgUS on my 367HO..... albeit at 65=1580rpm.heehee

Also at your stated useage, You can run a ton of cylinder pressure. The rules that apply to running WOT with a 4bbl do not apply to you. But you would need a decent closed chamber shape,like Magnum heads..... jus saying.