If I had complete control over every number in this case, I'd need to study the specifics and minutia more. I'm a bit methodical about stuff like this and I'd want to have data to find the sweet spot.

At a glance though, if I had to set a system, I wouldn't put all my eggs in one basket in terms of funding a UBI. I'd probably 'soften the blow' but using every means to fund such a thing. Decrease defense spending some, remove corporate subsidies entirely, have a steeper progressive tax, have the government fund via public capital ownership like Alaska, printing press, all of it. And I'd still maintain/establish certain single payer systems.

Ideally, I'd probably want there to be no one earning under 60k employed or not. Homer would likely get about 90k in the end with a UBI. 50% for his tax bracket +60k UBI. He'd make more of his money from a UBI in this case, but make plenty of money on top of that to encourage him to work at the plant assuming he finds his job fair or simply intrinsically rewarding regardless.

I would likely apply a UBI slowly though. It wouldn't be that I'd give everyone 60k at the outset Probably 15k and I'd use some of the leftover taxes to purchase government controlled capital for the first year to help fund it in the future. Then I'd probably regularly jump 5k every year (or maybe every other year) and stop at 60k. If the capital I purchased does well enough I might throw some excess earnings back on top of the regular UBI, but the 'output' would never drop below certain numbers.

The specific tax percentages would probably be variable depending on what is needed to fund everything, but there would be no subsidies or tax breaks. No loop holes. etc. It would be as concrete and simple as a progressive tax can be except that'd it would, like absolutely everything else, be adjusted for inflation.

This is pretty pie in the sky of course. Its ideal though and I'd always at least shoot for this.