VTAC director Kyle Lamb explains the features on the Glock basepad. You can purchase on VTAC website. Price is $29.99. This works for G17/22/34/35 and works for Gen4.
Link: http://www.vikingtactics.com/product-p/vt-sa-gbp.htm
Mag well is priced at $110. It also works for G17/22/34/35 but is not compatible with Gen4 Glocks.
Link: http://www.vikingtactics.com/product-p/vt-sa-mg.htm
From: VTAC