A 400sbc need heads specific to a 400sbc...nothing else will work properly...no steam holes will cause you to overheat...BAD!!! DO NOT use the 305 heads on your 400sbc!!! Go to the engine forum and get more info from those guys there!!
Intim, you are the only one Ive ever heard rave about how wonderful 305 heads are. I used em on a 350 once a few years back, against advise I should have taken, it was a pinging turd, sure, it pulled hard down low( as long as it wasnt pingin), but it was flat by about 4500 RPMs. Put the old 88s 76cc heads on, over all, much better.
The only guys I know who use 305 heads succesfully are the low dollar claimer dirt track stock car guys, & theyd rather use Vortec, but cant due to rules.
If you make em work, man, good luck to yea,... Ill pass