A 305 ci v-8 has the exact same block as the 5.7 l . though the mounting hardware might be a bit different, the swap is defiantly do-able. I would investigate getting the Lt1 engine fixed. That is a much stronger engine than the 305. The Lt1 will have a 4 bolt main as the 305 is a 2 bolt. If there is no hope for the 5.7 Lt1 engine and you must do the swap, the engine mounts will be the first thing you will need to examine to see if they will actually work. You may need to fab alot of parts but there is enough room for the 305. You will be disappointed in the performance of the 305 against the Lt1 engine but at least you will be going again. I am wondering what you plan to do about the computer control for the engine? Will you put the computer from the 82 Chevy in the caddy? You might consider investing in a hyper-tech tuner for your caddys computer. These are available at auto parts stores and will enable you to adjust the setting of your computer to more closely co inside with the application you will be setting it up for. You are in for quite the adventure with this project but again... it is very do-able