Thanks. Will you explain who modified it and why it's a RHD?
Um - no. Because it's not a Buick.
Working from memory is not my forte. My apologies to you and everyone else who worked on this puzzle.
However, it is a run-of-the-mill American brand, that is still in business, though somewhat day-to-day, of late. I have no idea as to why it is RHD, other than it may have been an export.
Because I screwed this up, I'll give you an exclusive opportunity to solve this one until tomorrow (Wednesday).