I've always wanted to stick a ~2006 duramax in something.
I think it'd be a super neat project.
I also think that no matter who does it it will be a longer project than you think. It'll also be expensive but I am assuming you know that. I was looking a while back and it seemed like you could get a used wrecked Duramax dwork truck for around 10k. That seems like it'd be the best option it you went domestic on the motor. Staying Toyota I don't know much about other than when I wanted to swap in a diesel (6-7 years ago) I couldn't even find one (1HDT) to buy on the North American continent. I hear it has gotten more difficult due to new import regs lately.
Either way, I'd vote for Redline. give them a buzz and see what they say.