Lots of good info here, but you need to understand that there are many variations possible when converting your car to Megasquirt EFI. You can use the Tbitz kit or design your own system which is much more involved.
You can read all about Megasquirt here:
http://www.bgsoflex.com/megasquirt.html
There are two different controllers, MSI and MSII. There are also different versions of code that can be loaded that add various functions. For example, the MSI standard code doesn't support EDIS, but you can load a version that adds that.
The Tbitz kit is designed to use the original intake runners, airbox, and throttle body. It uses the MSI v3 controller with custom code that eliminates the need for a TPS (throttle position sensor). So if you want to load a different version of the code later, you'll have to add a TPS. Not that big of a deal, really depends on your throttle body. But if all you're looking for is a good solid EFI, then there's no need to change anything.
I've been running a Tbitz kit for 4 or 5 years on my daily driver, an 82SC. I see a 2 to 3 MPG increase over the CIS (mostly highway driving). I added a wideband O2 sensor early on which lets me set the target AFR a bit richer for better performance. I have had no problems, starts easily hot or cold every time.
Your engine isn't currently running, if it has other issues you're not aware of it could make an EFI conversion much more difficult. You should also be aware that once you've done the conversion, the local Porsche garage won't be much help resolving problems related to the EFI.
If you still want to go the Tbitz route, download the installation manual from their web site. It explains everything about installing the kit. It can be done with the engine in the car or with an engine drop.