I have a L28 in my 240 with a ZX alternator upgrade. The belt fits correctly in the alternator pulley and the water pump pulley.

As you can see it does not seat all the way on the crank pulley. Do I have a L24 pulley on there do you think?

If they are in fact different then I guess I need to get a L28 crank pulley.

 

 

You could get a narrower belt.  But if you don't have slippage and the belt stays on there's no real reason to worry.  Looks like there's plenty of contact with the groove by the wear mark and the amount of wrap-around.  It's the small pulleys that usually have problems because there's less surface area in contact.

Is it squealing or slipping?

And the pulley V dimensions seem to be for the same belt anyway.  Look at the water pump pulley part numbers.  The crank pulley V dimensions are probably the same between L24 and L28.

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-240z-260z/water-pump-fan

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/water-pump-fan

Thanks for the reply Zed. I have been kind of busy. Here is a photo of the other pulleys where they seen to fit more flush.

I think it will be just fine too as you said. No high RPM's for me these days anymore.