318 build advise

I would like you to see something.
Go get a sheet of paper and strike a horizontal line across near the bottom, labeling it miles per hour, with zero on the left and on the right side, ending at 90 on the right.
Then divide that line into equal parts representing 10 mph each.
Strike a vertical line, up the left side, near the edge, and label it rpm, with zero where it crosses the horizontal line and 6000 at the top. Divide that line into equal parts representing 1000 rpm each.
Finally, estimate where 4400 rpm is, and from there strike a second horizontal line across to the right.
Now, lets put some data points on the 4400 line; which represents about peak power of the stock 318

You are gonna have to generate your data points in the following way;
You need to figure out your roadspeed at 4400 rpm, in each gear using your chosen rear gear and your chosen tire diameter. I will give you an example for 3.55s and a 25.5 tire;
The formula requires a tire roll-out so multiply your diameter by 3.1416 to get it. I will use a 25.5 tire which has a roll-out of 80 inches.
The formula also requires you to know your trans ratios, which for the standard 904/727, are 2.45-1.45-1.00
The formula also requires you to know the Slip in the TC, but we will just use 10% .
And we will need the rear gear; I will use 3.55s.
Here is the Formula
MPH= (rpm x Tc/roll-out)/ {the constant of1056 xR1 x R2}
where the Rs are the gears, and Tc is the roll-out
example
MPH = (4400 x80)/(1056 x2.45Low gear x3.55rear gear)
MPH= 352000/9484.56
MPH =37.1 mph; Likewise second at 4400 is 64.9mph, and direct is 93.5
Now we will just reduce all of those to account for the 10% theoretical slip in the Convertor, so I get;
33.4, 58.4, and 84.2 ; Plot those mph points on the 4400 rpm line.
Next strike lines from the zero-zero point in the bottom left corner, thru the data points and continue out to the 6000 line; all three times.
From those data-points on the 4400 line drop vertical lines to the lowest diagonal line.
What you should end up with is a sawtooth pattern representing your mph for any given roadspeed in any chosen gear, AND the vertical drops represent the shift points about thru the power peaks; not the actual shift points you would use.
Next, go find 32mph, and from there, strike a vertical line up thru the three diagonal lines. Do the same at 55mph.
Now you can see exactly what your rpm is gonna be in each gear, at those chosen markers of 32 and 55 mph.
Your engine is gonna be seeing those markers too, and if she cannot find a satisfactory rpm from which to pull from, in any gear at those data points, your combo will suffer a perceived laziness.
But Hang on; you have an automatic, so we have one more line to work out.
Climb up the Rpm line to 2200, or to about what your current stall is. Put a mark there, and connect it to the 4400 mark, and continue it out to 5500 and just let it hang there. Now, ignore the next nearest diagonal line below it, which would be correct for a manual trans (Allbeit slipping 10%,lol), make sure your 32 mph vertical marker-line crosses this new line.
Ok, I'm not making this graph here at home, so tell me at what rpm does the 32mph marker cross first and second gear, and
at what rpm does the 55mph marker cross second and third.
These two rpms per marker will represent the rpms at which you will be cruising, and the rpms to which Kickdown will go when you slam the pedal down. The first (32mph) is where you are gonna be most of the time, and the second (55) is for when you get stuck behind some slowpoke on the hiway, and want to know if it pays to force a kickdown.
You can plot your own personal markers where ever you like.
Now,
the analysis;
If your 2-1 KD at 32 mph , makes the rpm to be too high, then it will just shift right back into second, and there you are stuck in second gear at 59% of whatever it shifted out at. That gets old in a hurry, if your engine has no juice down there.
But if at 32mph in second, the KD into low makes the rpm to be too low,then you are again asking your engine to provide what it does not have.
Now maybe you understand about pressure.

So now, on the same chart, generate some new points using whatever rear gear you think you might entertain, or look at the numbers on the current chart, and theorize what might be a better rpm to be at, and generate a % difference, from where you are to where you want to be, and use that % to generate a new rear gear, then round that gear to the nearest physically available gear. And then generate a new graph.
If this all seems Greek to you, then PM me and we'll walk thru some examples together.