soko121 -- to help you narrow your searches down -- sounds like your SC is a "roller" that is missing both its engine and transmission and that you're looking for something a bit beefier than a stock 3L sc engine. If that's the case, here are my thoughts:
1) An SC was designed to use a type 915 transmission. Due to power handling limitations, the 915 transmission was not used in the 930 turbo (it used a different 4 speed transmission until 1989) and 1987 and later 911s used a g50 transmission (subsequently used in the 1989 and later turbos as well) that could properly handle additional power. The 915 can handle a fair bit more power than a stock 3L engine, but is a limiting factor with additional power. One cannot install a g50 in a SC without suspension/strut tower modification.
2) The 3.2l engine introduced with the 1984 Carrera is a very nice engine and, with stock induction, is, more or less, a drop-in upgrade for an SC. Unless recently (and properly) rebuilt, many used 3.2l engines are going to benefit from some level of rebuild prior to installation, with a top end rebuild (replacing worn valve guides, etc.) being the most common. While the engine is apart, it's relatively straightforward to bore a 3.2l engine's cylinders to 3.4l capacity and substitute in slightly higher compression pistons -- this provides a nice bump in power / drivability above the stock 3.2 (or 3l engine) -- one can similarly hotrod a 3L engine by boring it to create a 3.2 Short Stroke.
3) with the introduction of the 964 (and carried through with the subsequent 993), porsche increased the engine capacity to 3.6l -- the 3.6 engine is a "different beast" than the 3L used in the SC (or 3.2l used in the Carrera) and, while 3.6l conversions were relatively common upgrades, they're more involved than swapping in a 3.2 (requiring additional cooling solutions and exhaust solutions among other complications). Further, 3.6l engines are similarly going to generally require some level of rebuild prior to installation. So, generally speaking, a 3.6l conversion will be more expensive and involved than a 3.2l upgrade. Further, the additional power produced by a 3.6l (especially a modified 3.6l) will further strain a 915 transmission.
4) another consideration is whether your SC will be subject to (need to pass) emissions tests. In Colorado, my Carrera is subject to semi-annual "rolling road" emissions testing and needs to retain the emissions equipment necessary to meet rather stringent state requirements. Retaining stock exhaust and motronic induction allows me to comfortably pass Colorado emissions requirements -- other states (especially California) have additional hurdles that are even less mod-friendly.
Finally, I've found the pelican search function to be rather limiting and have found general google searches to be a more effective way to find responsive information from pelican (and other resources).
Hope the foregoing helps frame thoughts/ideas/searches for you. I have a 1986 Carrera and upgraded my 3.2 to a 3.4 using mahle "max Moritz" style pistons. I've found the upgrade to provide a noticeable improvement to acceleration and overall drivability
