The whole idea behind a "383" is taking a 350 and changing the crank from the factory 3.48" to 3.75". As stated the bore doesn't matter but to actually come up with approx 383ci you use a bore of 4.030 and a stroke of 3.75.
To come up with the stroke of 3.75" there are many options. When after market cranks were not as widely available as they are now people would take 400sbc cranks and have the main journals turned down to fit the 350 block... Now it is so much cheaper and easier to just buy a brand new one. Summit sells rotating assemblies all ready with matching parts and etc.
Your best bet would be to take your block to your machinist and tell him what you want.