318 exhaust manifolds on a 360
If I remember correctly the mini starter is not any narrower (horizontally) than a regular starter (not by much anyway). The main body is a much smaller diameter but the part of the starter that the manifold (77) was hitting was the solenoid. When I put the 2004R into my Cuda I found that the factory (large) starter was hitting the down pipe (because the TCI adapter kicks the starter out towards the driver's side) so I switched to a mini starter. But as it turns out the mini starter hit the down pipe in the same place (outside portion of the solenoid). Since the manifold was hitting against the starter solenoid on the large starter and the mini starter's solenoid is in the same place (space) it probably will hit the mini starter's solenoid also (especially with the starter even further out towards the driver's side). But, just in case someone else has been able to this (77 manifold in a a-body w/PS), I was never able to get the manifold in deep enough to know exactly where it would end up. In other words, there just wasn't enough room to get the manifold to seat. Since I couldn't get it to completely rest "flush" against the head (exhaust surface) I couldn't determine where I had to grind clearance. I would have had to remove the starter. I could see the bottom of manifold flange against the solenoid but if removed the starter I could never get it back in because the manifold would be right in the way. The only option is try a different manifold (there are many with the larger hole).
As many others have found, the main problem is the size (diameter) of the power steering box (and to some degree, the steering shaft u-joints). The complementary problem is the great size of the ports inside the manifold. Because of the manifold's large ports (which makes them great for power) it only makes sense that the overall size of the manifold is larger. It's just like the pipes on your headers...the larger the ID the larger the OD except the manifolds are heavy cast iron so they are proportionately larger.
I'll have some good pics later today to show what I'm talking about. You're asking some great questions!!!!, I'm sure others are reading and learning.
Treblig