I don't want to get into a huge debate here but having done LOTS of diesel conversions and LOTS of V8 conversions, the best choice is the V8. That is just my personal opinion. I personally am a huge diesel fan, especially the Toyota diesels. I have had lots of them and still own 4 Toyota diesels but the 5.3L Vortec V8 is the most economical conversion out there.
You will get more than 100k miles out of them (not sure where you came up with this #) and spend about 2/3 the cost of the diesel swap. Mileage will be about 20mpg compared to 22mpg for a Toyota diesel. With diesel fuel being about 20% more expensive than unleaded (where I am), it is more economical to drive the gasser. Of course this is not taking biofuels into consideration.
And then.... there is the parts issue. You are not going to find Toyota diesel parts very easily. Not as easily as you would a SBC.
Even though the SBC is a better choice, I'd still take a Toyota diesel anyday.