Rear sprocket question for 530 chain

[rdsarefun]

Just picked up a 74 RD350 and going thru it.  I am looking at sprockets and I cant seem to find a 40 tooth rear, only 39 tooth.  I bought a new DID non o-ring chain (530- 92 link) and am looking at new 15 tooth front sprockets, as mentioned earlier the only 40 tooth I could find is for an RZ. All the different sites I have found have 15/39 tooth combos.  Will the 40 tooth RZ fit or am I overthinking this and should just buy the 39 tooth?  Thanks in advance.

[rideitfast]

https://hvccycle.net/aluminum-rear-sprocket-rd250-rd350-r5-ds7-ds6-yr1-yr2-r3-rd350lc/

[Economy Cycle John]

one tooth on the rear makes marginal difference, the 39's that are commercially available are much cheaper, are steel and will last longer.