With a title mentioning a 60 foot centerfold, it stands to reason that there would be plenty of visual effects being used. Here's a rundown explaining how certain scenes were actually achieved.
Inflatable assets - after getting the approval from the Lindstrom clinic to use their beauty enhancement treatment again, Angel drinks her first vial, causing her chest to expand to the size of large melons, much to her delight. This expansion scene was accomplished by putting two balloons under J.J. North's shirt, with an air pump rigged to inflate them on cue.
Monstrous Side-Effects - after missing her nightly dose of beauty enhancement treatment, Angel overdoses, leading to a strange side-effect showing her face turning monstrous for a few seconds. This effects achieved by using a morph of an image of J.J. North, and the monster-head bust for her transformation. Computer effects then filled in the frames in-between the transformation to monster and back.
Heightened Suspense - We see Angel approach her bedroom mirror two times: first after getting out of bed, and then after overdosing on beauty enhancement treatment. Unnoticed to Angel, she's easily grown an extra foot in height. Mostlikely, some raised flooring (unseen by the camera) is on the floor, helping with the extra height. The clothing Angel is wearing is also enhanced slightly, to look like she's almost bursting out of it.
Angel's Big Debut - Wilson introduces everyone to the new, 60-ft Angel. This effect was created by filming J J North in front of a greenscreen or bluescreen background, and then compositing her into the beach scene. A cutout of the mountain range was copied and placed over the main mountain range, to sell the effect of Angel walking out from behind it.
Angle Attack - Considered a more inexpensive way to cheat size on film, the filmmakers shot J.J. North on a raised platform, looking over her shoulder. This helped sell her large size. Another camera angle is a low-angle, as seen to the image on the far right.
Dolly World - In order to sell scale properly in films where giants are prevalent, miniature items must be used for the oversized character to interact with. We see this during the film when Angel picsks up a small bouquet of flower or drinks from a small bottle of liquor.
Big and Bold - If miniature items are needed to make people seem bigger, oversized props are needed to help show the big effects they have on the little people. This can be seen with such oversized props as the giant lipstick made for Angel, as well as Dr Lindstrom's enormous tranquilizer dart that the over-sized Betty throws at Bob Gordon.
Forced Perspective Findings - For a long long time, a technique known as forced perspective has been used in many films that deal with giants The technique is used by putting the giant persons closer to the camera, and the normal-sized persons a ways away. The camera then sells the illusion of the giant Angel interacting with the little people around her.
Shrinking Effects - After being exposed to Dr Lindstrom's cure, both Angel and Betty shrink back to normal. Both J.J. North and Tammy Parks were shot against a greenscreen backing, then composited into the still shot of the street, with a layover of smoke effects. Using digital effects, the girls were also made smaller from their filmed elements.