Question on belt length with new pulleys

[Boxcars]

I just bought billet crank and water pump pulleys. The crank billet pulley is exactly the same circumference as the factory unit, but the new water pump seems to be about a 1/4" less in diameter. My original belt had some slack with the new pulleys enough so I didn't bother to start the car. Any opinions on what I should try first? 1" shorter or 2" shorter? TIA

 

[bison]

Try a 635 belt. Stock is 640

 

[Boxcars]

Try a 635 belt. Stock is 640

In the brand I can readily purchase, the next size shorter than the stocker is 63" (62.992). So, sounds like I should try the 1" shorter belt first. Thanks!