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It usually works fine to install the distributor with the vacuum advance pointing at about the middle of your passenger side fender. This should give you enough travel in both directions to set the correct timing. Then install the cap and pick your #1 cylinder as a starting point.
One tip - experiment a little with setting the timing on your SBC quite a bit more advanced than the factory book shows. The factory setting may be as low as 4 degrees BTDC. However, 12 is usually fine, and it might even take more. The compression ratio is really low on these smog-era engines.
Each time you bump up the base timing, set the idle back down to about 650 to ensure there is no mechanical advance being added.
Then run the rpm up and use a dial-back timing light to verify your mechanical advance. It should be about 18-20 degrees additional.
One tip - experiment a little with setting the timing on your SBC quite a bit more advanced than the factory book shows. The factory setting may be as low as 4 degrees BTDC. However, 12 is usually fine, and it might even take more. The compression ratio is really low on these smog-era engines.
Each time you bump up the base timing, set the idle back down to about 650 to ensure there is no mechanical advance being added.
Then run the rpm up and use a dial-back timing light to verify your mechanical advance. It should be about 18-20 degrees additional.
