Never seen a gear driven 305 only bigger V6 engines which have a 3 piece gear drive, I did such a conversion on my 478M V6. I'm using the 1966-74 305-379 type chain and sprockets, what was involved with this conversion was to eliminate the center idler gear which is lubricated with engine oil from the same passages that feed the front main bearings. This required capping off the center idler area with a 1 1/8 expansion plug and for extra insurance I also built a plate to cover up the plug, that will require drilling and tapping one more hole in the block and using countersunk fasteners to make clearance for the chain for best results. Though I did get away with using button head fasteners and it was just enough to clear the chain. I would really like to see the timing gear arrangement of your 305A, do you have any pics? One thing to note if you timing gear setup has just two gears and no idler that would mean the cam is spinning the opposite direction over a chain driven setup, so you will also need the 305E cam for the conversion.
