Magnum Heads On 340

I rebuilt my 68 340 block in the early 2000s and used magnum heads on it. After having one set with cracks I just bought new bare castings.
Back then all the Mopar magazines said that the 340 hipo exhaust manifolds bolt right on and they were right except you eight huge exhaust leaks. I made some plates that mostly sealed up the leaks but here I am 20 years later still fighting leaks on this thing.
Has anyone used the 340 manifolds on magnum heads and got them to seal? How did you do it?