Really, the only way to go guaranteed is to go with a full complete front clip or a known good source of motors. i.e. a place like heavy throttle. www.srswap.com
www.sr20detperformance.com

We can do your SR install for you over at secret services, for a 90 240sx we reccomend you get a front clip so you automatically get the gauge cluster and correct a/c lines and what not to make your swap as foolproof as possible. Call us for details.