If your target is only 400 hp then stick with the VN heads and get a basic seat and pocket port job done, on a 355 you'll make 400hp easy enough, you are better off spending your money on a decent hydro roller cam and make 400 rwhp.
I will be bumping comp up so chamber efficiency will be a big factor. I have a price on a valve job done on a newen CNC with chamber and port work which is $690 for the seats $1500 for the die grinder work then all the rest like guides valves and retainers.
The idea that I have is to keep velocity at max in the port and increase the VE with chamber work. So I can use the dual plane down low. I was looking at a 650 holly SS but read an article from David Vizard where he states that a 650 would be good for a single plane but a 950 would work better on a dual plane. If I went a 950 I would have to use vac secondaires.
All this means I'll probably hit closer to 500hp probably 460hp with the dual plane. I'm happy with less but for this engine to work it's going to need to rev past 6000rpm and it'll make over 400hp.
It used to have a massive solid roller and big valves with standard ports and a TP single plane running EFI. I didn't build that setup but it only made 420hp when the cam should've seen 540hp. I want to use a smaller cam less revs and make 400hp so the efficiency will be improved vastly.
This also highlights an issue I have with the iron heads I have, they already have big valves which need larger ports putting the revs up towards 7k when I want lower RPM to keep within the dual planes limits.
Basically I need the smallest ports I can find with the most efficient valves seats and chambers.