What do you mean by "a plate"?
Compressor brackets? For a Sanden-type compressor, I assume?
On a small block (early cast iron water pump or later aluminum water pump?), or a big block, or a slant 6, or??
I'll assume small block, cast iron water pump, since the one thing you DID say was "69 Dart".
Bouchillon has a bracket, if you have power steering: BPE A/C Compressor Mounting Bracket Kit Small Block W/ P.S - Bouchillon Performance Engineering
Or if you still need a compressor, Orininal Air offers compressor and bracket upgrade kits that hook up to the factory a/c: 65-69 Dodge/Plymouth Small Block A/C Upgrade Kit STAGE-1
Those add on A/C pkgs are for non A/C cars, the firewalls are different. You will have to fabricate something, something to simulate a non A/C firewall.