Hello Kevin,
I don't believe you would have any problems running that under a Linode 64.
The memory is the only thing that might eventually cause slow-downs, but there are some advantages (in terms of performance) from being on a big host machine.
The host machines utilize their extra RAM for cache of the file-system. So, let's say you have a large MySQL database that would benefit from sticking around in RAM rather than reading off the disk often. Well, even though your Linode thinks its reading blocks from its disk image, they very well may be coming from the hosts's cache, without any disk reads. So, performance is somewhat of a mix between your Linode and the host.
Short answer: I think you'll be fine
-Chris