I've installed a Toybox on an H55 in in my 1980 HJ45 Troopy. The install is pretty straightforward for an H55 or the H42 with the extension housing like the ones used in the Fj/HJ60 series. You need to shorten the transmission output shaft. Measure and cut with a zip disc. There are some threads on ih8mud.com with photos. Photos of y install can be found
here