Ok, so my dad is retired so yesterday I took him my project 85 vette to cruise around in until it goes to get painted. He has been driving my 1991 Buick Roadmaster for 2 years and kept her in great shape. She is a 1991 Roadmaster Estate with 305 TBI and a B&M 2500 torque converter. What should I do next? Vortec 5.7, nitrous, or a 4.8 LS swap? I need opinions here

Cold A/C, JVC head unit, and all new 9C1 suspension