AC Center Vent Repair....What Type Plastic

[spudder]

I have an original AC center vent assembly. It has some issues that need repaired. I want to do a plastic weld on the back side and add some material to reinforce each end around the screw holes. I think the plastic is ABS but not sure.
Anyone know for sure what type of plastic? Also what other plastic part I could use as a donor for filler material?
I've "welded" plastic before, just made sure to use a like material for filler.
Any help appreciated.