Assuming we are talking about the Chevrolet bolt pattern (not the Buick, Oldsmobile, Pontiac, Cadillac bolt pattern), either the top left bellhousing bolt or the adapter-to-block bolt immediately beneath it will have to be omitted, as they end up almost right on top of one another with both bolt patterns vertical. It is my thinking that this will be the case regardless of which bolt pattern is indexed. On adapters with no provision for bolts to the block above/external of the bellhousing pattern, I omit the bellhousing bolt. On adapters with the aforementioned provision, I have done either, with my preference being to omit the adapter-to-block bolt. I have not had any issues with either option. Starter nose clearance is fine. If you have access to a CNC mill, making an adapter from scratch should actually be faster and simpler (once you get it drawn and programmed) than modifying the OEM units as I have been doing, as it is a very time consuming and labor intensive undertaking. Unfortunately, this seems to be the only way (at the present, anyway) to get a vertical Chevy adapter. Good luck.