Need Help identifying the year for this Junker soon to be my next build

[Easter]

Bike came with a tank from an 80-81 DOHC Custom and I am not sure about the wheels, front forks and rotors. Maybe original,maybe an earlier customize attempt.

Help identifying it is appreciated.

CB750k - 2825257

 

[amc49]

Wheels, front fork and tank appear to be '80ish 750 DOHC Custom parts.

 

[Easter]

I once had a K2 but haven't worked with any of the later years of the SOHC bikes. It has a triangular oil tank which looks to be late model. Carbs were later type as well. Does anyone know the serial number sequence? CB750k-2825257 ? I will be replacing a lot of parts and hate to order any parts that will not fit.