In functional, I consider the AS5300 should able to support the required interfaces. However, it also depends on the required features that may not support in AS5300.
You need to check the supporting features in AS5300 that can work for you. Moreover, I have no information of the performance of AS5300, so I cannot sure that can work as the same as 7204 or not.
And, the AS5300 is EoL and the EoS (no hardware and software support) will be June 2007, it is fine for lab test but it will be an issue if it is for production network.
http://www.cisco.com/en/US/products/hw/univgate/ps501/prod_eol_notice0900aecd8052854b.html
Hope this helps.