The heat gun could be handy for the ABS. If I had 'welding equipment' I'd probably pass in favor of a MAP gas cylinder. I'd probably blow a hole in the sheet.
Cut the 60" dimension first (of course).
I cut a ABS scrap to size for a splitter in the Metro, 8x60". I'll be less busy in a week. It will have a chamfer like we've talked about, The radiator brace is the lowest point, which is nice.