What Chris Hammond said is the right answer, you just need to recompile the source again using the new dotnetnuke libraries.
I did that and it worked.
you have to do the following :
1- download the source of latest version of the blog from github.
2- open it using VS and remove the old reference for Dotnetnuke.dll , Dotnetnuke.Web (that actually used to have the dnn telerik wrappers controlls)
3- add the new library that contains the deprecated dnn wrappers controls for telerik which is (Dotnetnuke.Web.Deprecated.dll) of course you can get it from the DNN 8 bin folder.
4- now you need to go to Manage.ascx file and comment out the register directives for the following namespaces :
<%--<%@ Register TagPrefix="dnn" Namespace="DotNetNuke.UI.WebControls" Assembly="DotNetNuke" %>--%>
<%--<%@ Register TagPrefix="dnn" Assembly="DotNetNuke.Web" Namespace="DotNetNuke.Web.UI.WebControls" %>--%>
5- you have to register the new directive for dnn telerik controls that is in Deprecated dll you just added to reference in step 3
<%@ Register TagPrefix="dnn" Namespace="DotNetNuke.Web.UI.WebControls" Assembly="DotNetNuke.Web.Deprecated" %>
Kindly note that you have to do step 5 in any other *.ascx file that use dnn telerik controls .
6- final step rebuild the solution and you will get error because you have to update another reference for " System.Web.Http.dll" because the DNN 8 use the new one that Blog source does have the old. so Just remove the reference and added new "System.Web.Http.dll" from the DNN 8 bin folder.
7- Build again and hopefully it works.
8- go to the obj/release folder in the solution and you will see the "DotNetNuke.Modules.Blog.dll" complied just copy it to your DNN 8 bin folder and of course you will asked to replace the it with already old existed one.
9- replace the Manage.ascx file as well in Desktop Modules folder in your DNN8. and any other changed *.ascx files.
10- Enjoy , and please tell me in case anything happened ! :)