Me Again 
I did a project example with exactly what you want to achieve. here is the file:
MeshMergeExample.rar (145.6 KB)
I created an actor with 5 static mesh components inside:
on begin play I create a procedural mesh, put all the components I want to merge into an array and then proccess them with this custom functions:
note the last function destroys the original mesh component so we are sure this test is working
Enjoy!
Dany