Is this just a pipe dream?.
No way would you run an rb26 on an rb20 ecu.
As with all conversions wiring is the stumbling block of most people,but at the end of the day can be figured out when you have it all in front of you.
An rb26 is engine, so it's not awd, but it has a diff in the sump which you would have to chop off and weld up or perhaps just leave it there.
As for the gearbox (which one you didn't specify but you would have to be full retard to use the rb20 box) same theme, chop attessa shit off transfer case and weld up hole left behind
Then rip skids all day.