for me i'll go with low mileage halfcut if u could find one..
>100k km milage car, engine not the only one that kaput, the other wear and tear part should be replaced as well if necessary..
halfcut will cover almost of that if not all..

1jz and sr20det though they are good engines, u'll find difficulties is interfacing the electrical items..

Not that i'm skeptical on quality of malaysian mechanics but i'm sure the handling balance of already best on RX-8 will affected when swapped with those much heavier engine. I think that the main advantage of rotary, minimum engine weight thus contribute to good handling car, one of Japanese cornering machine ever