To be more specific, you can accept full BGP routes from a single EBGP peer and a single IBGP peer IF you have 256 MB of SDRAM in the router and you run the correct IOS and feature set.
The c3745 is easy as has accepted 256 MB from inception, the c2620XM will most likely require a ROM and SDRAM upgrade.
The IOS version needs to be the MINIMUM required to run BGP. I.e., don't run IP plus (which includes voice, etc.) or Enterprise anything. Since 12.4(4)T, Advanced Security has supported BGP4. I have had great luck with that feature set on 12.4(4)T or higher on both platforms you mention. For example:
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...