On my autocross car I have the eliseparts 40mm drop uprights front and rear.
The rears support radially mounted calipers only. I assume that is a good part of why most are using the 16mm drop or the sector111 uprights for the rear, because they let you use the stock rear caliper.
This is a problem because the vast majority of radially mounted calipers (especially lightweight ones) do not support a parking / emergency brake. As required by the solo rules you are suppose to have a redundant emergency brake.
So, what I did was source a 4 pot caliper with about the same piston area as the OE caliper from Wilwood that has a modification for the parking brake. This piston has roughly the same clamping force as our stock caliper but weighs several pounds less due to aluminum construction. The OE rear caliper is a heavy POS.
I think it is the same as what flyinmiata uses for their rear calipers on their BBK but I sourced the part from wilwood overseas. This required different rotors as well, as the calipers require narrower rotors. I ended up using rotors intended for a mini cooper that have the 4x100 pattern, after experimenting with 3 other sets of rotors for various 4x100 cars. Mini rotors were very cheap fortunately so that offset some of the cost of this endeavor. Also they weigh considerably less than Lotus rotors as they are not vented and smaller diameter.
This was still not exactly a bolt on deal, there are spacers behind the rotors to get them to line up, some washers to get the caliper to line up right, and then centering ring was fabricated so my hub where the mini rotor sits is mini sized. Different rear brake cables, both the hydralic and the parking brake cable were needed to as the fittings are different than stock.
Unfortunately I didn't keep track of the total weight savings exactly but it is somewhere in the ball park of 5lbs per side of unsprung weight.
If someone else wants to go down this path I could probably put everything together as a kit and save them a lot of R&D and money buying and returning parts.