I realize the SR makes more ultimate horsepower
I don't want to get into a big SR vs KA debate but this statement is completely wrong. In NA form the KA makes more power. With equal amount of bolt-ons the KA still makes more power.
If you go turbo the KA still makes more power. The SR can make good horsepower at high boost with lots of modifications. The KA also makes good horsepower at high boost with mods.
Check out KA-T.org for ideas about how much power the KA is making. To give a hint there are several people that make in excess of 500 horsepower on the KA turbo without even taking the valve cover or oil pan off.
The KA has a very wide power band with the power coming in at 1500 rpms and staying steady until a little over 6000. It makes for a very easy to drive and fast motor.
The only advantage I see with the SR is that it is aluminum and weighs 100 pounds less than the KA. The KA weighs about the same as a U20.
My suggestion is to get a 91-93 KA24DE from a 240sx. They are plentiful and cheap. I bought one for $255 and it had the computer, wiring harness, tranny, etc... I bought a second for $55.
If you just have to get the SR then I've got one for sale with a tranny for $600. It needs an ECU from a 91-93 240SX and it needs a distributor. I recently bought an 86 200sx and planned to put the SR20 in there but would sell one or both if someone was interested.