Can an Indy be safely lifted on a 2 post car lift - ie: lifting points under the "sills"?

Yes.
Why do you think it would be a problem?

just ensure the pads aren't touching the fibre glass

worst case just put some timbers running front to back just onside the sill / outer chassis rails and it will be fine.

Description

If its got the body on i wouldnt use the sills
|There can be a gap of around 5mm between the retun of the side panel and the chassis rail, it wont do the body asny good
I'd use the chaccis near the diff and below the footwells or the engine mounts

I just wanted to check, and use other's possible experiences before just going ahead and lifting.

I haven't taken a good look at the chassis to see whether there were "strong enough" members either along the sides, or out from the centre - I guess the cars are pretty strong, but their construction isn't like that of a "normal" car, so I just wanted to be a little more certain before going ahead.

Thanks for the replies folks ....... forewarned is forearmed