Whatever you do I would try running it on a test company.
Using SSMS run SELECT ITEMNMBR,ITEMNMBR FROM [dbo].IV00101 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
If you agree with this list then
DELETE [dbo].IV00101 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00102 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00103 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00104 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00105 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00106 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00107 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00108 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
DELETE [dbo].IV00109 WHERE ITEMNMBR NOT IN(SELECT ITEMNMBR FROM [dbo].[IV30200])
This should remove all the item master records.
After all these deletions run Check Links on the inventory series to see if anything went wrong.
There may be pother tables if you use bill of materials or third-party products.