After I built my 5.7 I primed it with a home-made pressure tank. I used one port to prime the oil system (heads, cam, etc) and second port to fill the oil pump.
What he said.
Take a look at this article.
15 Tips to Improve Your 727 Torqueflite Trans! - Hot Rod Network
I has similar situation and the orifice was already restricted. When I was putting the new Hemi in I tore the 727 down and added 3 springs to direct apply piston - that fixed the issue.
The longer coolant stays in the rad, the longer it will stay in the block as well, getting hotter... What helped in my case was bigger volume water pump and high flow thermostat.
What is your idle timing? Advancing the timing will bring the vacuum up.
On my 440 with Lunati cam I had to set idle advance to 22 degrees to get 15 inches of vacuum.
The vacuum might go up a bit once rings are broken in.
That was my main concern about Milodon pan. Even though I have c-body, std. big block oil pan for those (as well as a-body) has a cutout for the idler arm in full right turn. I did not want to mess with steering link so I made my own pan - I combined hemi and big block oil pans, retaining the...