340 intake on a 318?

Mid 70s means Low-compression 318LA. right? What will the 302 heads get you?
With a hi-stall it will be fine.

Had you chosen a Regular A833 manual trans;
in a Low-compression 318LA, the bottom end with the 340 cam would be soft to about 2400, then slowly start to wake up to about 3500, after which things get moving. But the heads will be done before the cam is, so..................
So the trans and gears you chose will be fine with a stall of 2800 or more. I've combo'd a few like that. I wouldn't call them rippers until you get into 4-series gears, but with 3.73s they're fun in first gear at least. And passing gear works pretty good.
The hard part is getting back up on the cam after the 1-2 shift. With heads done at ~5000, if you shift there, the Rs will fall to 56% or 2800rpm, way off the cam. So you will want to stretch it out a lil. Shifting at 5600 will get you 3150, still pretty low. By 6000 you're way down the choke-line but on the shift, she will come in at 3370 ........ see what I mean........
On a good note, the 340 cam has a long flat power curve; just what that trans wants.
Rear gears cannot help with this. They only change at what road-speed this happens. If you make the 1-2 shift happen at a low-enough roadspeed, before wind-resistance starts to get up, Second gear will work better.Hence the 4 series gears.
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I have run a low-compression 318LA with 4.30s and a 2800. Not a ripper, but fun none the less. Yes with Headers and a 4bbl, but with the stock heads and cam, on account of I knew about the choke-point. For which I just ran 5500rpm springs and short shifted the 904.
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The most fun I had with my 318 combo was actually with 2.76 gears, manually shifting up into third gear ASAP, and then letting the 2800TC/Thermoquad do their magic, moooooaning all the way to like 80 mph, still at ~2800 rpm,lol.
2.76s are like 4.30s except everything happens one gear later. What I mean is ;
2.76 x 2.45 (low gear)= 6.76 and
4.30 x 1.45(Second gr)=6.23.
So, First gear with 2.76s is just a tad better gear than 4.30s in Second. So then at 3500=40mph, or thereabout, they are a draw. (The big gears, in this case, only help get off the line). But of course take-off sucked, lol. I didn't care because at this time this was my winter engine and a DD, so the 60mph =2100 mattered more to me.
Eventually my son ended up with this combo and my 3.55s, which he soon swapped for 3.23s. ( I had a lotta lotta gears for a while back then.)