yes if you want them replaced
In the oil filler hole in the valve cover. Remove the plug (either twist out or pull out), add oil, and replace.
44 yrs old
about 4 quarts
Yes they should be if not you would only need to modify it slightly.
no
There were no Mustangs until '67.
In those years..they used 10w40.
.034
for auto and manual its 6 degrees BTDC
No, it's to wide, the largest that will fit is the 351w
5/8
.024 to .026 inch ( for the 200 cubic inch straight six cylinder in a 1966 Ford Mustang )