Sounds like an interesting swap, one that won't be easy and quick for sure. Fuel system will need changed to fuel injection with return line. Headders or exhuast will have to be custom fabricated. The motor mounts could probably be bought as a kit to bolt to the block but will need to be welded or modified to fit the frame. Cooling system, driveshaft, battery location, etc will have to be modified. Alot is gonna go into this sir, more than can be described here in a step by step process. This swap will be "learn as you go" type thing of what will work and what won't. Don't think it's not doable because it definitely is, but it will take alot of work and mods to your buick. Here's something I want to pitch to you...Have you ever thought about rebuilding your exhisting 430 to your specs with maybe a modern cam, pistons, head porting, etc and then adding a self tuning/learning throttle body injection system like E-Z EFI or holleys version? Would be much easier and only major mods would be to add a return line to your fuel tank. You would be able to enjoy the benefits of fuel injection and still keep the drivetrain intact with less work? Maybe even swap out the original trans to a 700? Just a thought.