the sight you're probably thinking of is jascoautomotive.com
the car you're thinking of is this, which isn't a 12a turbs but a ported NA motor.
mmmm rs5's!! thats what my rx4 will be wearing in about 2 weeks!:(
the conversion would be much the same as that of putting a rotary engine in one of the "sister cars", ie, 808/929/capella/121 etc.
the engine mounts for most rotaries are off the front of the engine rather than the sides like piston motors (13b turbo motors are the exception to this rule, as they have side engine mounts) You can see the front mount in that last pic.
this is done usually by using an rx4 cross member that bolts into the front sway bar mounts on the mazdas as the cars listed above also came out with rotaries being an "RX".
you would also then need a gearbox suitable for the rotor, ie, an rx7 series 1,2,3 box would be fine, and then modify a GB cross memeber to suit the rolla, and the tail shaft would need modifying.
next you will need a new radiator again s1,2,3 rx7 1 would do the trick (I actually have one of these, with oil cooler kicking around at home!! :D ) and all rotors need oil coolers aswell.
that would be all the hardest stuff, then you would just have to modify some wiring and the fuel system to suit.
you could pick up a standard 12a with carby, dizzy, alt, water pump etc (basically everything) for around $500 - $1000 depending on condition and the retention of the owner arse hole!!