I don’t know why you are tying yourself in knots over this. It’s an old, high mileage car. If it’s not leaking from the sump plug now, cut your losses and get an oil sucker. I use mine all the time. In fact, if I get a car in for an oil change with a top mounted filter, I use the sucker every time. Why mess about jacking the car up and fiddling about with an under tray if you don’t need to? I have no concerns using it on any of my cars and to be perfectly honest with you, with your level of skill going by the drive belt saga you recently had, I’d think very carefully about trying to tap a sump thread out without something going terribly wrong that could end up with you having to replace the sump. Sorry.
https://www.woodsideproducts.co.uk/...WDSuyNQObF9RoCLWsQAvD_BwE#174=&175=&178=&182=
https://www.woodsideproducts.co.uk/...WDSuyNQObF9RoCLWsQAvD_BwE#174=&175=&178=&182=