PSulivan,
That is a totally SICK (In a good way) conversion! Please keep posting pictures, and keep us informed of your progress.
On your question of frame strenght, I have installed 350 chevy's in two Toyota trucks, an '81 and an '84. The 81 was kind of a learning process, but worked okay - low power. The '84 had about 300 horsepower. The first time we got on it, and it hooked up, the left front wheel came off the ground, and never touched down again! So, from my experience with similar HP, but much less torque, and less weight, the stock frame was not up to the task - when being abused.
Other things I learned, were: The cooling system needed significant upgrading. The braking was scary because it was so fast, and needed to be upgraded as well. These items were obvious right from the start. I never got to any "long term" evaluations.
It was still a lot of fun.
Geoff