To all, I made some miscalculations in the statements below. Please read my edits in parenthesis
Honda made 3 different intake style runners [not including the differences of A and B]. These most likely had different part numbers but because the 77 (correction the year was early 78) was the only year of one style, that P/N was dropped in favor of the 75/76 (correction mid year 78 to 83) style.
Here is a way that you can at least tell the differences between them:
1) The 75/76 (75/77 is correct) has an outside diameter of not less than 1.660" and may be more depending on condition or corrosion. No step in the base flange.
2) The 77 (78 is correct from s/n 4000001 to 4019000) has an O.S. dia. of not less than 1.620". This too is based on condition. The 77 (correction the early 78's) and has a step in the casting flange at its base.
3) The 78/83 (correction later 78 at s/n 4019001 through 83) has the smallest O.S dia. of not less than 1.510". They too have a step in the bottom flange.
OK having said this the choice for 75 thru (correction77) because of their internal structure is the 75/76(correction /77) runners as long as you are looking for best running engine. If a Concurs d Elegance is your choice, you should try to use only the correct runners on your bike.
78/83 is the easy choice as the smaller diameters are quite noticeable. You might sneak on your 77(correction early 78) by using the later 78/83 runners depending on the knowledge of the Judges.
Also the OE finish from Honda on all years above is a very high luster polish with a fine grain around the diameter. Then clear coated with a good lacquer. The back side of each runner was not polished much without any grain.
Pistol and Moose
These errors are an unfortunate mis-reading of later data that I thought was correct and it wasn't until I looked at the 77 fiche and the 78 fiche each of the same year of manufacture that I found the correct information. Sorry, Pistol