3
V, 38, 37, 36, 34, 33, 32, 31 30 bytes
Àé r\2é/4é-òYphx$2Pòdd3GEòjlr\
Try it online!
I might catch up with Osabie. One byte shorter than Osabie. \o/ Tied with 2sable!
In other news, this is one of the longest strikethrough headers I've ever made.
Explanation:
Àé "Insert 'arg1'...