The timing is not a single number and depends on several factors including engine condition, the distributor's mechanical advance, and the vacuum advance. You cannot find the correct timing without a timing light and consulting your vehicle's specifications (often found in a sticker under the hood or in your owner's manual). The specifications will give a Base Timing value (usually in degrees BTDC - Before Top Dead Center) for a starting point. You then use the timing light to check your total timing at various RPMs to make sure your advance mechanisms are functioning correctly.
In short: You need a timing light and your vehicle's specifications (owner's manual, etc.) to determine the correct timing for your specific 1981 Caprice Classic 305. The firing order is definitively 1-8-4-3-6-5-7-2.
