Longer copy is acceptable. Including the full blog post text means a longer email, but there is a benefit to including the full blog text for your reader. You are offering them convenience by not making them click through to your site to read everything. You hold nothing back and give them everything for free, not even requiring a visit to your site. That can be seen as a form of goodwill, and readers often prefer the convenience of being able to read everything in their email client on their mobile device without having to open up a browser.
Do you have an older list that you suspect has mostly decayed? Create an engaging opt-in message and send it to your old list encouraging contacts who wish to re-opt-in -- promising to remove all contacts who don't respond. Though it might seem counterintuitive to remove folks from your email lists in order to grow them, emailing only engaged contacts could improve your deliverability and increase the odds of your email getting shared with those outside your current contacts database.