Making the summary block “Read More” link point to Source URL instead of SS post.

I'm trying to use code to make the "Read More" link on a summary block point to the Source URL in the blog post settings, instead of it pointing to the blog post URL on SquareSpace which is the default setting). I've seen other posts about this with code injection given for the footer, but none of those are working for me so far. 

Site url: https://turquoise-caterpillar-n778.squarespace.com/news
PW: WITCHES

You could hide the default read more link and use a text link in the excerpt to link to the source URL.

Thanks, Ziggy, I just did that and it's an option if all else fails. I would prefer my client not to have to do that on every blog post though.