Ok hold the phone;
I have a 367 that by it's trapspeed is making 430 hp. I also run a manual trans but with 3.55s.
I know exactly what it takes to run 400hp. and I know,
yur gunna be sorry, unless you swap to 4.30s.
Here's why;
Your starter gear is 2.66 x 3.23= 8.59
Your rear tires are likely to be ~24.5 tall.
To make the 400 out of that combo, with the factory heads, my guess is that you'll need a cam of about 248@050.
The lowest rpm that your 400hp engine will sustain, with that cam/cylinder pressure, in gear, is gunna be ~650 and it will take a helluva tune to achieve that. Thus, the slowest speed you can ever drive is 5.5 mph; And with 400hp on tap, yur gunna need to be a hevckuva tuner, again, to not have the engine get jumpy on you down there.
So, forget parading. and you will be forever slipping the clutch, to drive any slower. And from every light and stopsign, you will be easing it out. Then, when you get to Second, the split is 72%, so say you are just driving "normally", like I do, lol, and you take First out to 2800....... cuz you know, you don't want to sound like a Mustang.
Ok so on the 1-2 Shift, the Rs will drop to 2000rpm........ and your big cam/low-compression/750/Torquer engine, is so far off the torque-peak, it will labor to get back up out of that hole, unless you give it lots of ignition advance, and then you get into detonation.
So then, IMO, you need to rethink the entire combo, else you are gunna end up like me with thousands of dollars worth of parts on the shelf, that did not work.
So again, IMO, you need to ask, a different question, such as,
"what would work with the parts I already have," or
state your budget and let the guys put it together for you.
But above all, state what rear gear you will not consider going bigger than; cuz those 3.23s with a 2.66low A833, are gunna be your limiting factors, for NON-WOT, First gear performance......... and every time the car stops, you are looking to drag yur azz thru first gear again which won't wake up until 3500@ 30 stinking mph, unless the tires are spinning, and that ain't gunna happen unless yur mean to the clutch.
IMHO
a good STREET build for the parts you have, and for your light-weight Valiant would be around 300/330hp.
300 for Iron heads, and 8/1 Scr
330 for alloy heads, new pistons at 10.5 or more, and maybe one size smaller cam.
I made 330hp with a 223/230/110 cam, and that was enough to take my 3650 pound Barracuda to 106 in the quarter, on street tires. Scr was 11.1 with those alloy heads.
I'm still not liking the 3.23s but I'd at least give them a chance. You better have a posi.
Happy HotRodding.
This will have enough grunt to pull that 8.59 starter gear;