Best use of new sales page?

What's the best way to integrate an "old school" sales letter into a large, content-based site with lots of traffic without jeopardizing my rankings and search results? Converting on this site has always been a struggle.

Now I have a new, single-page sales letter of the "old school" type: no header; no fancy graphics; big, brash headline; and no menu nor links.

I think it will convert well but it's not compatible with my site. I'm considering two ways of using it:

1. Redirect my current index page to it. This will capture nearly all incoming traffic but once there, there's no getting out.

But what happens with spiders? Will the rest of my site be invisible to them?

2. Format the new page so that it's consistent with the rest of the site. Remove the menu from the header area and offer just a few links at the bottom of the sales page. This should retain my search rankings but there's still a risk that visitors will drift to other pages when they reach the bottom of the sales page. I'm hoping it's good enough that this won't happen, but who knows at this point?

Am I missing anything better? Thanks for any suggestions.