Shifter bushings
www.autohausaz.com
The floor:
However if you dont want to spend $3500 find a used/junk car and cut out what you need.
Your other option is to make one. A good hotrod custom shop should be able to make one with all the support channels in it.
You can also make small patch panels and fix just the bad areas.
Check the firewall below the fuse box and in the inner wheel well in that area.
If your floor is rusted then it's likely that the inner rocker panels and jack point are bad also.
Please post pictures of your rust areas.

1977 Mercedes 450SEL 6.9 Auto Trans Shift Linkage Bushing | AutohausAZ
The floor:
1166161567 online kaufen | eBay
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However if you dont want to spend $3500 find a used/junk car and cut out what you need.
Your other option is to make one. A good hotrod custom shop should be able to make one with all the support channels in it.
You can also make small patch panels and fix just the bad areas.
Check the firewall below the fuse box and in the inner wheel well in that area.
If your floor is rusted then it's likely that the inner rocker panels and jack point are bad also.
Please post pictures of your rust areas.