Are ARP head bolts really needed for a mild build?

Personally I wouldn't call your 340 a mild build, either way the ARP's are cheap insurance considering you don't know how old the existing bolts are or whether they've been stretched one to many times. Nothing lasts forever IMO. For 7K I'd be replacing the main bearing and con rod bolting also, same reason.

x2!! Why would you risk it when arp bolts are so cheap?

At the very least,buy thier rod bolts. Those take mega punishment.