fitment queries?

[Noodle_Soup]

hey guys, am wondering on the possibilities of fitting the gearbox off of a s13 (jap spec...SR20 not CA18) to my silvia, as im finding the CA18 box off the 13 bit short in 5th, dunno might just be the rev counter reading wrong but my car still pulls like a train when approaching redline and keeps on going past it, for fear of total destruction i was looking at somthing slighlty longer and remembered that my 180sx pulled 150mph (on my private race track officer!) at around the 6,000rpm mark. i dont think my 12 would reach that speed but would be nice to know that im not gonna terminally injure the engine if i get to carried away on a high speed test!!

any info greatfully recieved.