If you’ll pardon my pointing it out, it doesn’t sound as if your father is particularly disabled.
He’s not able to do his former job. Actually he wanted to. OSHA forbid his presence in the workplace with his heart condition. The company insurance forbid his working that job as well (liability). His company (where he got his disability) didn’t have any other jobs they could offer him (wanted to offer him at his age) and just wrote him off to disability. It was cheaper for them to do that than fight a wrongful dismissal suit or pay the extra liability the insurance company wanted.
Liability and health insurance were prohibitive when he looked into opening a fix-it business on his own. And OSHA wouldn’t have permitted HIM to be on the premises doing work with his heart condition at that time.
30+ years ago (he’s ~80 now) there weren’t the same level of medical interventions in heart disease there are now. He had his massive MI right before the introduction of the clot buster drugs. He’s still prohibited from lifting anything more than 20lbs or walking up more than 1 flight of stairs in a certain amount of time. He’s got all sorts of ‘assistance’ equipment in his shop to help him. All the lifting and supporting stuff. He’s got kids and kin who help him move heavy stuff if he has to. He’s not on a schedule with anything so waiting several days isn’t a big deal. Since clotbuster drugs there are very few people with his kind of heart damage anymore. And most of the ones that had that sort of damage are dead now.