If you strive for a certain look of your presentation, you have to stick to that look’s design rules. When building a slideshow with a PPT template, pay attention to color palettes, fonts, and construction. Don’t get stuck at recreating color palettes specific to vintage epoch, better get into color psychology to select the color supporting your branding goal and think how you can fit it to vintage design. Do some research on the technology in use during the epoch you are going back to before picking the right font for your presentation. Make sure the construction of your design is consistent, and there are no 3D graphics or high res photography across the slides in vintage style.