Toyota Repair: 3SFE - 5SFE, head gasket problem, computer control system

Question
I had previously asked you about the overheating condition for my 91 MR2 non-turbo, and sure enough I have a head gasket problem.  That was the problem that was keeping me from driving it but it has alot of other problems too (valve cover leak, oil pump check valve broken, front main seal leak, rear main seal leak, and worst of all possible excessive blow-by gases from blown piston rings).  Thats alot of work to do all of those items so I'm gonna try to save myself alot of labor and just replace the whole motor.  Now I've had a little trouble finding reasonably priced 5SFE motors.  I've seen plenty of 3SFE motors though.  I hear that its the same block just slightly different bore/stroke.  If thats the case it should be a totally compatible swap, but nobody seems to know for sure whether it will fit easily or not?  What do you know about these engines? Any big differences that would cause me troubles?  Also there are 2 different versions of the 3SFE I've seen.  The obvious visual difference in the pictures I've seen is the valve cover spark plug wire holes are square instead of the round ones like my motor.  You know any difference of those motors?  Thanks for your help.  

Answer
The 3SFE motor will absolutely not interchange with the 5SFE, not only are they physically different but the computer control system is also different and on top of everything else it is against emission control regulations to do this in all states of the US.