Out of all the engines you listed the only two I would get are the O.S 21 tm and O.S 18 tz. All the rest are not direct bolt ins, meaning you need to either modify your engine mount and some how make more room for the new big block or purchase the Newera big block conversion kit. The Jato is a light weight 2 wheel drive truck that really does not need all the extra torque of a big block motor, those motors work better with heavier 4 wheel drive trucks. The smaller motors are lighter and are able to rev out to a higher rpm you just need to have enough displacement to pull the weight of your Jato. Most people are saying the O.S 21 tm is very powerful and are happy with it, my vote would go for that one if your looking for the most power and speed with less hassle. Watch your slipper clutch, that much power will be hard on your tranny.