Which heads on 1994 magnum block

Have a 1993 dated magnum block going in a 1971 dart. Speed pro h116cp pistons, undecided cam yet. Both heads were cracked like normal. Trying to decide if should go with speedmaster aluminum heads or get some magnum replacements. Block has the oiling for la style heads. Would like to be around 400 hp, or little more. What would be the best and easiest route? Is there alot of geometry issues with the speedmaster heads? Is there any good flowing magnum cast iron heads available anymore?