Hammer??? 
It looks like one of the pads may be out of position in the housing???
It should be a "no problemo" sort of fit!
It is interesting to see that your Goose casting is different than what I found in #878, Yours kinda sorta has Pantera-ish features, AND Goose uniqueness.
The Goose does not have the U-joint right out the back door of the shifter housing......but rather further back on the shaft......
See if you can't put the arm in place without the shifter box in the car, so that you can see where the lower ball resides when in place between two pads.
The shifter should slip thru the hole in the shift rod....with no issues.....ie check your shifter bushings to see that they are in proper position and not out of place.
I do NOT recall where those black foamy looking things resided.....CRS disease!
Steve
PS: In my "Oops I'm doing it again" post, towards the end pages, I found some materials that I used for the heat shields. Check it out. If you can't locate it, ping me back......I have some of that material still. Possibly the rivets and a die for the rivets that I had machined up..........as well.
