I was looking at the micromac website http://www.micromac.com/products/performerpro.html and was wondering something.

If these accelerators can be used on a Mac Plus under System 6, is there any reason why it cannot be used on a 512K, or at least a 512Ke?

Most of these boards add up to 16MB RAM, which would certainly solve any RAM issues with the 512K. For that matter, it should work with the 128K, then.