Gsr belt or type R belt. B16 has a smaller belt and wont fit. Ls belt must be used if an Ls water pump is used. But if you use a b16/type R/Gsr water pump, then just use the gsr one.
And btw, changing the head on a gsr which has a 41cc-ish cc combustion chamber to a b16 head which has a 42cc-ish combustion chamber will actually lower your compression b/c the gsr has lower compression pistons compared to the b16.
both engines factory make the same compression
b16=larger combustion chamber with larger slug pistons
b18c1=smaller combustion chamber with smaller slug pistons.
So you will lower your compression and the cams in the b16 are also weaker than the gsr. Like 3whp which is 8-10 flywheel hp. You may make up for 1 whp b/c of head flow but the poor mans type R is kinda wierd to me. Better than an Ls/vtec but wierd. Less compression than a b18c but slightly better head flow with weaker camshafts. What does one make really. I'm kinda curious. It still has a 10:1 cr instead of 10.2:1.
I know you know your stuff so none of this is an insult, just figured I'd throw the info out there.