Hikaro

Hey all,doing a headswap on my D15Z4,got a D16Y9 head for a good deal so thats my plan for now. My question is what size timing belt do I use? Do I stick with the D15 one and swap out the timing gear or use the D16 one? Also I know there will be a tooth difference between the two so will swopping the gear do anything to affect the cam duration? I know its not a firebreather so not going crazy yet,got plans for a B20 lump in the next few months so this is just temporary till then,you know get me from A to B. So any assistance would be most appreciated .

Thanks Nate