340 Build

I got about the same engine except it's a 3.58 stroke. She went 93 in the Eighth at 3467 pounds and at 900 ft elevation, and on 87E10.............. with 3.55s.
My ace in the hole is the 3.09 low gear that adds 16% TM (TorqueMultiplication) over the 2.66 factory gear, turning the 3.55s into 4.12s. If you have a 2.47 low-gear box, yur toast with 3.73s, cuz 2.47x3.73=9.21 versus my 3.09x3.55=10.97
My combo is happy with 3.23x3.09=9.98.
But your 340 with that cam is torque-challenged, so I would stick with a starter gear of ~11/1 which calls for 11/2.66=4.14s, or 11/2.47=4.45, making the average dead on 4.30s....... just like YR said.
If you go 4.30s , that will increase your launch-TM by 4.3/3.73=plus 23%, so your engine will sorta feel 23% bigger. If your engine currently feels like a 273 at launch, now it will feel like a 340,lol.
But there's more; all your shifts will come sooner in mph, so you will be putting down more average horsepower over distance, and that is what you are not feeling.
If you're not willing to go into the 4.xx ratios, then you have two options; 1) a bigger engine, or 2) an engine that thinks it's bigger at normal street speeds. And the latter usually means an earlier closing intake valve to trap more cylinder pressure. There are a few ways to do that... a hydro cam with faster ramps,a smaller hydro cam, or a fast-ramp solid-lifter cam.
93 in the Eighth, Mr. Wallace translates to 115 in the quarter, which could be just into the 11s.

I hear the guys harping on degreeing the cam, and they are NOT wrong.
But my experience, as a streeter, with the three cams I have moved around, is this; with street gears and street tires and a manual trans; it makes almost no difference where the centerline is, within +/- 4*. With 3.73s your 340 should burn right thru first gear to over 50 mph, and second will take you to 70@6000. So you have a window of opportunity to time the improvement of 20 mph, which is less than 2 seconds. You'll never see that accurately repeatable on a stopwatch.
I said almost no difference because; even if you were out by 4 degrees, the pressure difference is a tic over 4 psi on the cranking cylinder pressure, and the power peak might move 50 rpm. So, because you burned right thru first gear, who cares if the cam is out. And in second gear, who cares about cylinder pressure in a streeter, with 3.73s cuz;50mph is ~4300rpm, right on or near the torque-peak and your butt dyno cannot feel a 4ftlb difference. So that just leaves the run from 50 to 70, and the 50 rpm change is only gonna make a few hp difference at peak on a combo like yours; you won't feel that either.
The only way to measure an improvement is to track test it, with a timer, and minimal tirespin.
And besides; changing the cam-timing just trades high-rpm power, for low-rpm power. and vice versa. It ain't much, and with a clutch, you can compensate for the loss on the start-line.
What you can't compensate for is lack of cylinder pressure and lack of TM, at low speed, around town. Here, torque is King, and the right starter gear makes all the difference.
Ok but having said that, if you installed the timing gearset with just one tooth out, yeah you'll feel that lol. But I've never heard of anybody doing that....... besides me,lol.
You can check the cam installed centerline without removing the entire front end, but it's nearly as much work on a SBM. You can check the Split-Overlap at the lifters. It's not as accurate,maybe, but it will put you very close. Close enough to prove the dots were dot-to-dot.....or not,lol.
A 4* lack of ignition timing can lose more power than 4 degrees of cam advance lost. And too much timing, causing detonation will kill power too...... so prove your timing.
FYI;
My combo has a 230/237/110 cam. And yes, I feel it is bigger than I need. But it is so much fun. My previous cam was a 223/230/110 and I liked it better. The 3.55s were the gear of choice with both, buut; recall my trans has the 3.09 Commando gearset. The gears are all different except the M/S first, so you can't just swap the gears;you need a set.
The ratios are:
3.09-1.92-1.40-1.00; versus
2.66-1.91-1.39-1.00; versus
2.47-1.77-1.34-1.00