Toyota TSB Information TC99002
Toyota issued a Technical Service Bulletin on this problem in 1998 for the 1997 T100 with the 3.4 V6. It's number is TC99002. I'm not sure if anyone's gone through this with their local dealer, mine said they probably won't honor that anymore because of it's age and if you've made it to 150k miles (in my case) head gasket failure is likely to be a normal failure due to age and mileage. If anyone's contacted someone at the Toyota HQ or their local district let me know - I'd like to see if they'll do this for mine.