There is a guy on the 67-72chevytrucks.com fourm that fabs and sells brackets to put an power booster on your truck. I got the one for my 61 and will be installing it very soon. It uses existing hole in the firewall so there's no need for drilling.

1961 GMC 3/4-ton with matching 10ft Fleet Aire camper (restoration work in progress)
1970 Volkwagen Squareback (restored for daughter's 1st car)
1958 Fleetliner 14ft runabout (restored)
2003 F250 4dr 4X4 V10
Pix on Flickr