I'm only familiar with the GTV6 arrangement. Not Alfetta bumpers.
As bayalfa said, finding the nuts is as easy as he described. But removing those nuts are not so easy. The studs are molded into the rubber impact strip. And most of the nuts are usually frozen to the studs. If you somehow have obtained a new rubber portion, you may be OK. But you will normally strip out the base of the studs, in trying to remove the nuts. So, if you are trying to repair what you have... you might find yourself screwed!
I found out the hard way. Even using a lot of penetrating oil. In the South, you may have less corrosion there... so just a warning. Good luck.
I have the bumpers off my '78 sedan if you want to look at abck side and/or play with rubber removal. I fear that front steel member is badly corroded as I can see a swelling & separation beneath the rubber.