I used an R30 SF for that one once, and I nearly fell a sleep, except I started to understand the wayward ways of that monster car...
The 3000GT LM '99 (689hp) can be won only through the Laguna Seca enduro. The other 3000GT LM (GT1-style, 618hp) can only be won by getting all golds in the I-C license tests.
By the way, the Celica Rally Car ('99-style) isn't a bad "other" car, because it's as fast as any 4WD car, save the Escudo. If you can't win the FTO LM, it's just about as good, and will win all but 2 of the rally races (never matched to the Cultus, though).