Update Contact with custom activity outArgument

I am creating custom activities that will return outArguments that include a targetingID for each subscriber. I’d like to use the update contact activity within journey builder rather than an API call to make the updates. I have been able to see that the outArgument returns the correct data but cannot find a way to pass that along to Update Contact. Has anyone been able to pass information from a custom activity to a journey builder default activity?

Leads converting to Contacts in Journey Builder

How do I handle the use case in a Journey where a lead in Salesforce can convert and become a contact, in which case we still want the customer record (lead or contact) to go through the same seamless experience as part of the journey, but also want to ensure that the communication includes any updated attributes that would now live on the contact level.
Translating this better from a Salesforce schema perspective, is there a way to start referencing contact attributes when a lead converts while still going through a journey. Or is there a way to have a contact start the journey at the point where the lead converts?