Hey Kats,
I had a bumper restored by a company in Melbourne who were able to straighten it out really well, better than I could with a hammer/dolly.
Photos before:
https://www.viczcar.com/forums/topic/12896-wtb-rear-bumper-2-seater-s30z/?do=findComment&comment=176976
Photos after:
https://www.viczcar.com/forums/topic/12896-wtb-rear-bumper-2-seater-s30z/?do=findComment&comment=186589
Originally I was going to put this back on my red 72 (HS30 10552), but it was too nice compared to the rest of the car. So I swapped the bumper off HS30 00150 onto the red car and have kept the restored bumper for HS30 00150 when that car is repainted.
They did such a great job, I would not bother buying the aftermarket bumpers on offer. Instead I'd have them restore the originals! I think the finish is probably better than back in 1970.