What year is my 13b?!? Also need a lightweight flywheel
 

I know it is a 74 to 78 but I have not a clue what exact year. I bought a 79 sa rx7 expecting a 12a. Next day I was home and opened the hood to see it was a 13b. I've heard there's different port sizes. Also looking for a lightweight flywheel steel or aluminum. I already have a counterweight. Thanks! Here's the only pictures I have.
https://cimg7.ibsrv.net/gimg/www.rx7...6eda7c1aa0.jpg
https://cimg8.ibsrv.net/gimg/www.rx7...b908a9d71c.jpg

the engine is 74-75. the large framed MAZDA script is the most identifying mark about these engines. i'm running a 74 engine in my 84.

Rotor housings for sure are 1974-75 13B. Check the stamping on the front iron to see what they say. It should be stamped 3B if they are the 1974-75 irons as well. It might be a built engine with a mixture of parts. You would need a rear counterweight from an automatic rx4 or repu to fit that engine for a light flywheel.

and i think the rear iron has R5 cast into it? there's also the letter Y in these early engines but can't remember at this moment.

R5 irons were used in the later 76 to 78 13b and in the SA Rx-7 12a engines along with the Y irons. They kind of mixed and matched in the days of the SA 12a. With the early script Mazda rotor housings the irons should be 3B stamped.

I have a flywheel... PM me if interested

The best advice I have to source flywheel is Atkins rotary ,yes on the houseing should ba 3b stamp,that definitely SA motor

first gen rx7 didn't get 13b til 84 with the introduction of the gsl-se. 78-83 were all 12a. what he has is an old school 13b form the early 70s.