yer fire wall stay's , check out sssute's build thread with all the parts ready to go did it in 9 days
your in perth, if ya want to drop over one day and check out my ute thats in the process of getting a sr20det put in it . it might give you a better idea of wats need'd but hears a quick run down , mines been off the road for 2+ years in that time its had a ca18de then ca18det then a second ca18det now a sr20det is about to go in ,
i have the maddat diff, brake booster ,crossmembers , mazda rx7 brakes with coilovers , fmic , 3inch zorst , fuel cell n surge tank , so pretty much every bit has to been swap'd for bigger stronger parts , some things people say you can get away with like the stock diff n only upgrage to stanza brakes , but i found the diff need's to be lsd or you'll paint black line's with out knowing it , and the stanza brakes where scary imo
cheers