if youve got no programmable ECU's or anything then theres not alot of point getting it tuned.
as far as timing goes, you can set that yourself, get hold of a timing light and make sure its at 20degrees btdc (i think thats what it is for an RB25)
when u say tappits do you mean lifters? RB engines have hydraulic lifters and they can make a bit of noise. unfortunately they cant really be repaired without alot of work. you can dull the sound a little by using a thicker oil... the other thing which could be ticking is either an exhaust leak, or the injectors may be noisy. ive heard a couple of SR's with noisy injectors but its probably nothing to really worry about