Well, I guess I can't really say for sure on the Toyota, except that everything I have ever had made in Japan was so very, very expensive on parts. I also live in probably much different circumstances than you, that is I am in a rural area and there are no Toyota dealers for many miles but the Perkins and Cummins engines are very easy to find parts for here. And of course the price for parts is comparatively reasonable.
I guess after reading the other posts maybe the other smaller engines might be something to consider but the 6354 Perkins weighs less than 1000 lbs (without accessories) as does the Cummins. I don't think that is so terribly heavy considering the old Chevy 6 cylinders where by no means light. You didn't say if this is a 3/4 ton or not. If it is, I would think the B series or Perkins would work pretty well.
