400 BB build issues

Link didn't open for some reason...

What is halfway on the gage? 160? 180? 200?

Do you have a fan installed? I can't see one...

Fan Shroud? Don't see one of those either...

Stock radiator? I can't tell but the one in the pic above looks stock; and I'm going to hop on a limb and say a 400 probably needs significantly more cooling capacity than a slant

Bottom rad hose staying open? (not collapsing at increased RPM) I've seen this too many times...

Timing? If it's too far retarded, you'll have poor throttle response and mixture still burning leaving the engine...heat soaks the heads...

I can't say with any level of familiarity, but there have been some guys on here that had issues similar to yours with the 440 source water pump housing if memory serves...