EQ Heads and stock rocker arms?

I know a 360 cam make 400 with that combo, maybe a bit more. So a 340 will be nip and tuck.
My 367 has a very similar cam, and powerpeaks at about 5400. In your 340 it might peak a tad higher, but with those heads the peak will be hard to find exactly. In any case the 727 has a pretty steep 1-2 split and the 2-3 is a bit better.
Looking at the ratios; 2.45-1.45-1.00, I see the splits are .54 and 69. So the 2-3 shift will probably need to be around 6400. This will make the outgoing power, near to the incoming power.You will need to fine tune it from there. The Rs will drop from 6400 to something like 4400. So in this gear the powerband requirement is 2000 rpm. The 1-2 will require an even higher shift-rpm.Knowing this, don't forget to mod your oiling system to survive that.
With 400 hp you will probably trap around 95mph,so 4.88s will get you about 5800 with 28s,;sounds about right. I ran those for 93mph.
The 750AG is right.
I run the 1110 springs with 1.6 rockers with the Hughes HE 3038AL that advertises .539/.571(1.6). I threw in some extra shims of .030/seat IIRC, and it Revs happily to well past 7200 with no issues. I run a 7qt pan and a HVpump. So the springs are Ok too. I had lots of PV clearance; but you'll have to check yours. I run otherwise stock Eddies.
My philosophy was; Since I have to buy adjustable arms anyway, it might as well be 1.6s. I didn't buy then for the extra lift, but for the extra dwell; up to, on top, and over, the nose. Seems to be working. Mine is a 68 Barracuda DD.
If you can get your 60ft down to 1.7 or less, 7.5s are easy. At 2.2 60ft my time was 7.92@93@3467#