I think for the budget minded individual looking to do a V8 swap, the 75-78 Datsun Z is a better choice than the more rare and expensive, not to mention weaker/delicate 240Zs.
The 302 is the way to go, because of the availability of the motor/transmissions, the power upgrades, the lighter starting weight, the front distributor (better weight dist), and how easy they are to work on.
The JTR rear tranny crossmember with the exhaust cutouts is actually designed and built for the Chevy 350, but with redrilling only a couple mounting holes, will accept the Ford T-5, so that is a plug-n-play item.
As far as stiffening up the body/chassis on a 280, I would definately go with front and rear strut tower braces that will also improve the handling a bit. When looking at potential cars to do this swap into, look real close at the entire length of the frame rails for rot (take a screwdriver and poke around), or areas where the car has bottomed out and the rails are crushed. In either case, I would replace the section of rail with new just for the piece of mind it would give me.
It seems like the most common area for frame rail rust is visible in the front wheel wells behind the front tires where all the road debris, water, and salt have hit it for years.