GM full-size cars got quite a bit shorter starting with the 77 models. You might want to measure the wheelbase on that 81 frame before you lay down your money. If it is too short, look at 76 and earlier frames.
I am assuming you need a full frame because you said the back end of yours was rust-damaged. If you really want just the front end, look at a subframe from a Camaro/Firebird or Nova/Omega/Ventura/Apollo, etc.
Rau
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