So what the difference between a flat 8 and a 180 degree V8?

Here is something few people realize, simply because they accept the status quo: Humans are not the slightest bit objective or logical or rational. We are truly subjective creatures and our decisions, both individual and collective, are more "art" than "science." Porche has perfected a single engine/car design over seventy years of development. Does it make sense? Probably not. Does the internal combustion piston engine make sense? Probably not. We'd all be better off if we had moved to a Wankel engine or better yet, a small turbine decades ago. But we haven't. I think it probably has to do with our appreciation of the reciprocal action of a piston going up and down in a cylinder. It's Freudian.

I do not know 911s very well (944 owner) but does anyone know if these will fit into 996s? If so, they could have a lot of sales from people with RMS and intermediate shaft issues.

I've heard this before and I don't understand it. If the cylinders are horizontally opposed, where does the V angle come in?

They should fit as the 996 engine bay is very similar to the 997's.
The biggest problem would be the cost.

The Ruf engine alone is probably worth more than most 996's!

A better option for the 996 would be an LS1 V8 like in so many early 911 conversions.

I haven't seen any converted yet but it's only a matter of time IMHO.

A true boxer flat engine has a crank that has one crank pin per connecting rod. 180 degree V engines, as they are called, share a crank pin for cylinders like any other V engine (SBC, etc). This is how the Testarossa was designed. So even though the Testarossa motor is often said to be a boxer 12, it isn't.

But people who want spoked wheels (or wooden spoked wheels) on their 911 will NEVER want a V-8...

Not if you take out a lot of wt. And that appears to be where Porsche is headed.

Light weight solves a host of performance, emissions, and env'l problems - all at once.

Wait & See.

I'm hoping Porsche goes the Lotus route as well.

Extruded & bonded aluminum chassis structures are where it's at.

You say that like you are a chasis engineer or something.;)

I think I need to phrase my position as a question so we get a yes or no instead of straying:

Would anyone be opposed to Porsche building a 911 with a 6.0 liter flat-8 engine (Roughly 450lbs, or same as current 911 engines)?

I would not be opposed to that, just don't call it a 911.