Looks like it is.
Try to make it spin. If so, definitely lose.

What brand are those mufflers?

"Maybe this is where split carbs would be beneficial vs racked given the angles."

Split for more power and higher revs.

Very nice report!
Keep up the good work!

"I ordered a double banjo bolt with bleed nipple attached (second pic) as I have found from experience this makes bleeding up a whole lot easier."

+100, really makes you life easier.

Keep up the good work!

CV slower response than flats but reliable and MUCH cheaper.
Ad carbs ok but I also recommend 750 ones for better chance of correct jets.

.For the front brakes, I'm wondering about running a double line from the master cylinder for a hint better feel on braking. Well, that's my thought at least.

Double line, how does that work?

Not sure about 750 Paso gearbox ratios but 15/40 or similar most seems to like.

Nope, still enjoying desmo at 67.

If RR is faulty, Shindengen is recommended. Done by several here and can be found cheaply from Jap bikes second hand.

Great find and looking good!

Hate to be a bore, but I`d mail Marvic to hear if they are still safe to use.
After all, they're 30 years old mag wheels...

"Or is it maybe 40 mm header pipe from some other Ducati bike (SS or Monster)?"

My guess too.
600-750 had smaller I/d.