Yes -
Let's clarify a couple of points --
In Class 1 and Class 2 AMA Carrier, you can enter just about anything so long as the engine displacement limits are observed. You will get high speed points, low speed points and landing points and multi-engine bonus points if requirements are met. You MIGHT get Scale Bonus points, if your model meets the requirements. The Skyshark, being a profile, gets no scale bonus points but can be entered - just as any profile model can be entered in Class 1 - and flown.
In Profile Class, you can enter just about anything so long as the minimum wing area (300 sq. in.) is met and the engine displacement (.36xx) is met. You will also get high speed, low speed, landing points, multi-engine bonus(if eligible)and, if scale bonus is earned, the 10 Scale Bonus points. Note that the Skyshark - as designed - doesn't meet the minimum wing area, but if you were to add a strip to the trailing edge that gets it up to 300 sq., then you can enter it in Profile class. Any CD will also judge the outline of the wing to 'closely resemble' the prototype and give you the 10 bonus points also. (You can still enter this model in Class 1, since you would have a .36 or less engine).
In Nostalgia, you can ENTER any plane that fits the 1974-75 rules for Class 1, Class 2, or Profile class - again engine displacement limits apply in all 3 classes and the 300 sq. in minimum applies to Profile. (So, you cannot enter the Skyshark in Profile unless you get the wing up to 300 sq. in.). So you CAN ENTER the Skyshark in Nostalgia Class 1 and (maybe) Profile (if the wing area is 300 sq., and the engine is a .36). You will get your High Speed, Low Speed and landing points. However, in the 1974 rules, there are no Scale bonus points in Profile, so you will NOT get Scale Bonus in any class of Nostalgia Carrier.
Now, in Nostalgia Carrier there are also 20 bonus points for using a non-schneurle engine and 100 bonus points for using a 'historic' model - designed/published prior to 1978 - including the Skyshark. If you build it stock - which it seems you wish to do - then you will get the 100 bonus points for the historic model in Nostalgia Class 1 but it won't meet the minimum wing area for any version of Profile. If you add the wing area you could fly it in Profile but it won't get the historic model bonus (in any class).
Clear (as mud), right?
To answer your question then - Yes - build it stock and power it with anything up to a .40 and you can enter it in Nostalgia (and modern) Class 1. You forfeit scale points (100 in class 1). You get the 100 Historic bonus points.
Use an old K&B .40 or any non-schneurle and you get the 20 engine bonus points also.
It cannot fly in any Profile class with less than 300 square inches, though.
(Bob answered while I was typing - and what he states it true. If you get some documentation from him that a modified version of the Skyshark was flown prior to 1978, and that you modify yours according to his documentation, then you will also earn the historic model bonus in either Profile or Class 1)