As Juicebox was written from the ground up for a different platform than SimpleViewer (HTML5 vs Flash), Juicebox and SimpleViewer share similar but not identical feature sets. As such, it may not be possible to exactly match a SimpleViewer-Pro gallery using Juicebox-Pro (there may not be direct equivalents for all SimpleViewer-Pro configuration options in Juicebox-Pro), although you should certainly be able to get close.

If you want to have two columns of thumbnails to the left of your main images and vertically aligned to the top of the gallery (like your existing SimpleViewer gallery), set:

thumbsPosition="LEFT"
thumbsVAlign="TOP"
maxThumbColumns="2"
maxThumbRows="7"

All these thumbnail options can be found in JuiceboxBuilder-Pro's 'Customize -> Thumbnails' section.
When thumbsPosition is set to either LEFT or RIGHT, the number of thumbnail columns is fixed at the maxThumbColumns value whereas the number of thumbnail rows is variable (up to the maxThumbRows value) depending on the dimensions of the thumbnails and the space available in the user's browser.
For reference, here is a list of all Thumbnail Options.

To replicate your existing SimpleViewer gallery, you might also like to set:

captionPosition="BELOW_IMAGE"

The caption area will be positioned below the main images and the width of the caption area will match the width of the currently-displayed image.

You can also change the gallery background color, change the thumbnail dimensions and add some image padding to match your existing SimpleViewer gallery if you like.

Here's a demo gallery using the suggestions above: https://juicebox.net/demos/pro/default/ … Padding=50

You could certainly tweak the gallery further if you like.
Here's a list of all Juicebox-Pro Config Options.

Please note that all the options I've used in the demo gallery above (except for backgroundColor) are Pro-only options which are supported by Juicebox-Pro but not Juicebox-Lite (the free version).

I hope this helps.