I know this has already been explored and maybe tested to death, but I had a play with some IKP baseplates, more just for show and tell, but this is what I did yesterday, when they got here.
https://www.ocdskateshop.com.au/products/independent-ikp-baseplate-setIndependent Inverted Kingpin Baseplate set, or IKP for short
OCD Skateshop had 20% off trucks and wheels including these new Indy baseplate sets, so I got some as people had been asking about them. I also got some new Indy trucks and after they arrived today, I did a little swap and measure of the normal standard 149 trucks with the inverted kingpin baseplates, as per pictures provided, along with my personal preference set aside for this experiment (as I prefer normal standard kingpin assemblies to IKP versions).
The first thing I noticed was the inverted kingpin itself doesn't have a particularly long thread, so I tightened these down as far as they would go, which wasn't that much with the truck still feeling fairly loose overall. They sit a few mm below the standard kingpin at that height, but apart from that they are almost the same in terms of the baseplates, with maybe a slightly different angle of the kingpin to the normal ones, but it was minimal. The IKP has a special nut that sits inside the baseplate, so there is no way you will be taking these out to change them over, but you can always use any other brand kingpin to put into them.
The other interesting thing was to see how much clearance there was on the IKP set compared to standards, as per the last pic showing the angle of them when sitting on the hanger and resting on the kingpin, with the IKP version definitely having a lower profile.