Have a look athttp://www.keil.com/dd/search_parm.asp
Enter the required minimum specs (e.g. 8051 127 byte RAM, 8k ROM, 5 Volt supply, 2 timer) and you get a pretty overview about the available chips
including the their packages.
By the way: There are some issues converting a circuit from original 8051
(NMos) to CMos.
Note that in the NMOS devices (8051, etc.) the signal at the XTAL2 pin
actually drives the internal clock generator. In the CMOS devices (80C51,
etc.), the signal at the XTAL1 pin drives the internal clock generator.
Hope this helps