unless that RB20DET is worked quite heavily, i'd suggest you look at a larger engine like a VQ30/35DE/DET/DETT.
or even an RB26DETT and stroking it with a 400cc stroker kit.
a smaller, 2ltr, I6 wont be able to hold it's own in a heavy american car, basically, go for displacement and japanese power.
If i still owned an excel.. It'd look like this: