The automatic attribute `node["kernel"]["machine"]` will hold `x86_64` or `x86` (I'm guessing) so you could create two attributes for the two download links.

```ruby
default["apache2"]["mod_pagespeed"]["package_link"]["x86_64"] = "https://dl-ssl.google.com/dl/linux/direct/mod-pagespeed-stable_current_amd64.deb"
default["apache2"]["mod_pagespeed"]["package_link"]["x86"] = "https://dl-ssl.google.com/dl/linux/direct/mod-pagespeed-beta_current_i386.deb"
```

And then in the recipe:

```ruby
remote_file "/tmp/mod-pagespeed.deb" do
  source node["apache2"]["mod_pagespeed"]["package_link"][node["kernel"]["machine"]]
  # ...
end
```