Very difficult with frame on. Don't know the extent of grease and rust. Grease is removed by lots of ways. Several techniques will be necessary. Choose according to extent of grease and rust.
Big chunks first, then:
1. Degreaser and pressure washer.
2. Harbor Freight air needler.
3. Wire wheel.
4. Manual labor with various tools.
5. WD40
6. I use spray on gas for grease.
Rust:
1. Wire wheel
2. Media blast
3. Needler
4. All manner of discs
5. When grease is gone and rust is down to clean, tight, surface rust, spray with Rustoleum Rust Reformer. Then paint with your favorite chassis paint.
POR has a system you may want to check out.
