Let suppose in your module layout file you can write the code as follows to override the left and content block:
<block type="yourmodule/yourblockclass" name="yourblockclass" template="yourmodule/index.phtml" />
<block type="yourmodule/yourblockclass" name="yourblockclass" template="yourmodule/left.phtml" />
let me have opportunity to explain the above code:
Let suppose that your website url is like that:
the above url will triger the above code and you will have your left and content section.
Let me know in case of any issue and more help.