Grills and frames HELP!!!

[Stm3784]

so I have a couple dumb questions, I have been collecting parts for 78 k20 build. I picked up a grill from a boneyard, it's cracked and the lower center mount is broke off, otherwise it's ok. Can I use it or will the vibration tear it apart? 2nd and most important. The frame I want to use is the original frame from this truck, it's been in the elements of PA for 20+ years. I looked at it today, still looks pretty solid except where the crossmembers are, they're rotted. Now the question is, can these be replaced? And can I use any 3/4 ton crossmember from 73-87? Please let me know. This determines if it gets scrapped or not. Thanks