Holley
Your vacuum secondaries are on demand so to speak. To quicken the response to demand you can get a Holley spring assortment and change the spring under your secondary diaphram. You will never see the vacuum secondary open all the way in the shop just wacking the throttle as there is not enough demand on the carb to open all the way.
To convert to machanical secondary you would also need a secondary accelerator pump to go along with that. It would be better to sell what you have and purchase a mechanical secondary carb. JMO