Welcome to the N board.
First off you can buy an adapter that converts your pto shaft from 1 3/8" to 1 1/8"
See first photo.
Secondly, they do make the longer pins for attaching the arms onto the brackets under the axle.
They look just like the ones in the second pic but are about 3" long.
This site likely has both items. You can call them at 800 853-2651 and ask. (I like to support our hosts here) Otherwise Tractor Supply should have them too. I bought both items at our local Fleet Farm store.
Those Dearborn/Danusers are good units, as is anything built by Danuser. I had one for a few years but sold it in favor of a later Ford model when I went all blue.
Kind of PIA to mount on your tractor though.
If you don't find the long pins let me know.
I'm pretty sure I still have the ones I bought laying around here. Have no use for them now.
I would send them your way for the price of shipping if you need.
My email is open.