Radiator didn't fit quite right

[Freddo]

I know this is pretty minimal compared to some of the things I see in here, but thought I would put it out there. My old 67 Chev longbox (283 with a turbo 400) has done quite a bit of work for me (on my days off) through the last summer. It's been running warm for a while now, especially on hot days or when I'm hauling a load of dirt or a trailer with some concrete. I've just taken it easy when I see the temp gauge climbing and figured I would replace or repair the radiator. The radiator is the 48 year old original, so it has every right to be tired. I spoke with a local radiator guy and he thought he could 'rod it out' and give it a new lease on life. He figured cost would be $125-$150 for the rodding out which seemed very reasonable as long as it did the job and to do a recore would be about $400. Ouch!
I have heard good things here about the way the Spectra 369 radiator fits and considering the inexpensive price (about $165 at Rockauto), I thought I would give it a try.
Got the radiator in and went to put it on. It doesn't quite fit. The rubber holders that fit inside the upper and lower mounting brackets won't fit over the larger flanges on the new radiator. We tried taking the rubber mounts completely out and it would fit, but that sure didn't seem right and I was pretty reluctant to start carving on these rubber mounts to make it fit.
My thought is to send the radiator back to Rock auto and to do the work on my original radiator, but thought I would see if anyone else here has had this problem with the Spectra?
Is there a real easy fix? Inexpensive mounting brackets that would fit?
I know there are some other radiator vendors on the board here and has anyone tried their products and had a true fit without carving up their mounts?
I took a couple of pictures to show what I mean on this. (I had already put the new radiator back in the box so it's a little tougher to see.)
All advice appreciated!