Is it a real 67 RSSS
 

The 4P code was not used at the start of production at either the Van Nuys plant or the Norwood plant.
Van Nuys started using the 4P code on the SS350 cars in September, but Norwood didn't start using the 4P code until October. Early Van Nuys SS350 cars and Norwood SS350 cars built before October will not have the 4P code to verify that they are SS's.
The 4P code can indicate either a SS350 or a L30/M20. Usage of the 4P code with the L30/M20 is believed to have started in the late December 1966 / January 1967 timeframe.

The very first 1967 Z28's and L78's were also coded 4P; the 4L and 4K codes were then used on the remainder of 1967 Z28 and L78 production.

The lack of a 4P, 4L, 4N, or 4K code indicates the car originally had a 327 (assuming the car had a V8, as indicated by the VIN). The only exception is the early SS350's noted above.

Edit:
4P= 295 hp 350
4L= 290 hp 302
4N= 325 hp 396
4K= 375 hp 396

Since your tag is October Van Nuts it should be either 4P, 4N or 4K.

What engine did it have?

I just looked up the SS option since it worth way more then the RS appearance package. GM did not combine codes. All SS's would have the correct code regardless of other options.

Reread my post:
"Van Nuys started using the 4P code on the SS350 cars in September"
"Since your tag is October Van Nuts it should be either 4P, 4N or 4K."
If it does not have the above codes it is not a SS.

The code for RS is 3L That would be group 3 letter L. There can be a lot of options in a group, see below. (Note, GM did not put the group number one in the beginning, no number assume one)

Example 3rd line:
WD 2LG 3SL
W= Tinted side windows
D = Power Convertible top
2 = group
L= M20 (or 21)
G = Console
3= group
S= Interior Decor GRP
L= Rally sport package

Example 4th line:
4P 5Y

4= group
P= SS350

5= group
Y= belts all deluxe

Looks like a full blown Clone.

I cannot seem to find a group 2 W like you listed. Is it possible its a M?

Picture of Trim Tag?
Agree, no 4x on tag, no SS
Got to have 3L for RS pkg

I will state the obvious, if its not numbers matching then does it matter? IMO the only real advantage to a "real" SS without the original drive train is that some day you could find the correct casting parts and fabricate numbers matching. Yes I know real cars are worth more but if you can get a well done clone for less money, I would.

Keep in mind only the 1967 has the detailed cowl tag. There is no way to prove 100% that a 68 or a 69 is an SS. No document that a school kid could not fake. You can order "original" paper document with any options you want for your Vin. They even remake cowl tags now. So even 67s can be faked.