440Source Stealth heads. I'm building a 440 for my D200 which will see moderate towing duty and decided to go with those heads because at $1200 a PAIR, I could easily spend just as much or more to have the original 346 iron heads machined and all new hardware put in. And I'd still have heavy iron heads that hardly flow enough air for a 440 cubic inch engine. Hell the ported Edelbrock RPMs on the 360 SBM in my Duster probably flow 40 cfm more than the best unported iron BB head which is a joke. 440Source claims the Stealths flow 280-290 cfm OOTB.
I listed my 346 heads on bacefook marketplace a couple weeks ago and have gotten zero interest; nobody wants to mess with iron heads anymore since decent aftermarket aluminum ones are so affordable.