Looks like the hit was high enough to spare the suspension. You won't know for sure on the frame until the bad sheet metal is out of the way.
Welding a new front end on will be a ton of work and the sheet metal damage pushed back all the way to the firewall. If you have to do any work to the firewall, I'll try to find another cab to work with. Since you know all the good stuff on your rig, I'd consider buying another 620 that's fairly staight, but mechanically bad and swap all your good stuff to it.
Unless you have the tools/abilities to cut/weld the entire front end back on, you need another rig. That isn't anything that you can pull out with a comealong.
By the time you buy all the little parts at the s/y, you could probably find another 620 for about the same. With scrap metal being up around $220/ton, you'll make some money back on the left over pieces......they're worth the same even if they're crunched