[Puzzdre]

I wouldn't recommend it. I got heater core from Lancia prisma and it has plastic top and bottom, with plastic onlet/outlet. If you want to rip the plastic top you'll have to find a good way to make metal top with barbs and to seal it properly.
I think that rad you talkig about is similar to this one I got, and know this: it is not just rip off the top and solder barbs, if you look at it closely you'll see that there are multiple water pipes connected in paralell. That is what makes metal top hard to make couse you have to separate the area inside the top in two chambers (in and out chamber)

IMHO, just use what you have!