There are more than a few models and engines for the Stealth/3000gt. All were 3.0L but there was a SOHC, DOHC, and DOHC TT. R/T doesn't necesarily mean DOHC TT engine. R/T AWD has the DOHC TT and is what you could compare to a 3000gt VR4.

Couldn't tell you much about head and intake swaps. You'd really have to have a set of both parts to compare to your stockers.

 

http://web.tampabay.rr.com/redroby/3liter/

Here is a website of someone I know that was building up his 3.0L Duster, until he sold it, but his website contains alot of good info