unless your doing crazy things with compression, head design and such spark plug gap is more bout the ignition driving it, not the engine that it is installed in. .045 gap will give you a cleaner, more complete burn than .035, in theory anyway. The more modern ignition components generate more energy than the components from 1969 allowing you to take advantage of the wider gap. If your worried or concerned do the .035 gap that was specified for 1969, it will run fine. Is there verifiable information to support using the larger gap? Yes. Is it earthshattering, life changing different? No. It is just simple research that .045 is the recommended gap for the EFI and ignition set up.