[Kevan]

What ballast placement strategy do people follow to keep these cars upright?

As low, and as wide as possible is not a bad place to start...........initially I would not bother with ballast  along the centerline of the chassis,....perimeter weighting will require less total weight, to achieve the same effect 

Cheers
Chris Walker

Yes and no. wide & low definitely calms any car down, I know it's your favourite ballast layout from photos of umpteen cars you've shared...I prefer the same ballast layout.  I do find only out wide makes the car a little lethargic in direction changes so that's the reason I like some right in the middle of the car also.