The new dataset will be cataloged with the parameters of XY.A.ABCDDMS
The system copies the following DCB information from the
data set label:
If you code any DCB subparameters after the dsname, these
subparameters override the corresponding subparameters in
the data set label. The system copies from the referenced
label only those subparameters not specified on the
referencing DD statement.
Answer to your question:
The length of the new file will be same as of XY.A.ABCDDMS
The new file for which DCB has been defined as DCB=(XY.A.ABCDDMS,BLKSIZE=32760) will be created withe same DCB attributes (except BLKSIZE which will be 32760) as that of already created dataset XY.A.ABCDDMS. The LRECL of the new file will be same as that of XY.A.ABCDDMS.