340 build up

Before I invested a dime in cast iron stock heads....especially if you need to install larger valves , I'd look at Eddies , RHS X heads ( these are iron ) , Airwolfs or similar.
By the time you hot tank , surface , port , do guides ( it will probably need them ) , valves , springs and a good valve job..........let's hope the seats are all good and there are hardened exhaust seats or you can add another good chunk of dough.
Yep......add all that stuff up.
Better mag those castings too.
I am not trying to discourage you. Just prepare you.
Wit aluminum heads , you can run a little more compression too.
With Eddies , 10 to 10.5 : 1 , cam in the .500 ish and 235 @ .050 numbers.
Air gap and 750 to 850 d.p. 1 3/4 " primary headers. Good converter.
Stab it and steer.
My 340 was milder than that cam wise , with an M-1 and 750 d.p. , 1 5/8th primary headers ( it was an early A and these came with it ) , loose converter of unknown heritage and a 3.91 cog. Ton of fun on the strasse and quick enough to maintain respectability. I whooped up on a buddy's '65 Vette with a 327 / 350 h.p. stick shift car severely , so I guess it was kind of quick. No idea of the weight , but it was full interior and frames tied , 7/8th offset spring hangars and SS leafs. Nothing fancy.
Like others have said , be SURE what you want and expect.
Then do it once.