Sorry no one responded to you
I have factory a/c in my car and don’t have experience with after market a/c units. Regarding Vintage air; a friend added one to his 67 Mustang with the r134 and had it installed over a long weekend. I was not part of the install but can state that the air was cold and worked well. He did change out the alternator and changed the fan blade. He had the unit under the dash so not a stock looking interior but his wife will ride in the car now. He has since found a factory a/c dash that he plans to install but is trying to work out the changes necessary to use the existing blower motor and new dash vents. I think he is planning to make these modifications in the winter when the car is in storage.
This mod should be documented cause I am interested in how he is going to make it work. Bottom line is this one Vintage Air unit works well with r134.