Doing 100 to 200 a upgade;home has existing
2w/gd sub-panel(60a)What's a nice way of convincing h/o, also a contractor, to go for the right way,(3-wire)and for my info, what's best
way to finish sub-panel; iso a new ground bar? Never done this; drill and tap the back of box for the bar, right?

Why would the homeowner NOT want to upgrade to a bigger service panel?? and yeah you need to separate those grounds out. and if you buy a new sub panel it should come with a new ground bar.

Read all the small print on the labels, there might be a catalog # for a ground bus. If there is, there should be some holes in the can for its installation. of course, if you're dealing with an antique, that info might not be there.

Tom

I would get rid of the sub panel and extend those lines to reach the new larger upgraded panel if at all possible. If you do need to mount a new bar then yes drill and tap!!!