Scott,
This is a very difficult question. Marketo's RCE will help with this as it does work on first touch and multi touch.
In Marketo, the FT gets acquisition credit and subsequent Programs before and during the Opp can also get credit. How you structure this will depend on the exact Report. So if you want FT Lead Source, you can do what Adam does. That's usually built into the system as well.
I see nothing wrong with giving a Program credit 200 days later, I very often advise people to use a 270 day window. It all will depend on your reporting.
See this article
http://perkuto.com/blog/marketing-automation/marketing-attribution-model-for-marketing-automation