copying articles form one blog to another?

[rj]

When I began a political blog last year I had a friend help who liked putting up off topic articles of the odd and bizarre. They turned out driving a good share of my traffic. I decided to begin a new blog in that theme. I would guess there are 300 such articles (and jpgs from google images) which about 20 still get appreciable traffic. Evergreen

My plan is to leave those articles on the original blog and copy them over to the new one changing the titles and updating the text some. On the old articles add a link to the new blog saying something like FOR MORE OF THIS GO TO. For the 20 or so that drive good traffic I want to do 301s to the new blog.

I am unsure how I should date the articles I am copying over. Keep the orginal dates or just start adding them in real time. An SEO issue? As is leaving the old ones on the old blog rather than deleting them.
Any ideas on how best to do this in regards to SEO matters?

Thanx

RJ