ECU's are not interchangable.
That write up makes it sound easy to bolt a 20v head to a 7afe block, that is the easy bit as the holes line up, getting it to run and produce decent power is the hard/expensive bit.
The 7afe is an "economy" engine, lightweight rods, 6 bolt crank, fuel efficient head.
You can fit a 4age head and gain about 20bhp or fit a 4age engine and gain 20bhp.
Fit a 20v engine Silvertop or Blacktop and gain 40-45bhp.
To build a good 20v with 7afe block [short version]you should get custom rods, ARP bolts/studs, race bearings, use 20v pistons [block has to be machined to right height] flywheel should to be dowelled to crank, Porshe timing belt to drive cams, stand alone ECU, and a nightmare of wireing.