Which Mac Pros will take any of the components currently in my G5 Quad?

The reason for my posting here rather than in the Mac Pro forum is that I need to lean on the expertise of the Power Mac experts in this forum.

While I'm extremely happy with the current performance of my G5 Quad, I can foresee the need for a Mac-Intel machine in the future in order to run modern Adobe software like Photoshop CS6, Illustrator, and InDesign.

As I'm strictly on a bargain-basement type of budget, I'm beginning to toy with the idea of buying a second-hand basic Mac Pro that could use any of the components I have in my Quad. I know the SCSI card is hopeless, but what about the video graphics card, the RAM modules and the drives?

My thinking is to start looking around for a low-priced, used 64-bit capable Mac Pro.

Any input will be most appreciated.

2.5 GHz Power Mac (PPC) G5-Quad;

16GB RAM (8 x 2GB DDR2 SDRAM PC2-4200U-444);

mutant, flashed 550MHz nVidia GeForce 7800GTX 1,700MHz 512MB VRAM;

ATTO ExpressPCI UL5D LP SCSI card;

Mac OS X Tiger 10.4.11 and Leopard 10.5.8 boot drives; Spotblight, Dashboard and Time Machine permanently disabled;

dual 22" CRT monitors;

USB wireless 'n' available but connected to the Internet via wired Ethernet;

FW flatbed scanner;

2 SCSI scanners (one tabloid-size transparency scanner and a film scanner);

various internal & external HDs.