Book says it is a TO which is a 0-Grade with Twist barrels.
This is a shining example of when the "book" is wrong.
However, I can see where the confusion might lie in attempting to grade the gun by the barrel steel listed in the order book.
The subject gun does not have the typical Damascus Steel barrels that were normally used on most Parkers of Grades-1 or 2 and on up the grade scale. This gun has a type of Laminated or Twist barrels used on very few of the higher graded guns of the day and was probably shown in the order book as Twist but this is obviously a Grade-6 or A Grade Parker. A few thousand guns earlier it would have been a $300 grade.
See the picture of another higher grade Parker with similar barrels.
....nuts!! oversized!
See an earlier discussion of this type of barrel steel here
http://parkerguns.org/forums/showthr...lish+Laminated
.