You should be able to approximate something using an EQ before the amp with a heavy boost of the frequencies around 1-2K.  From what I understand there was a an element of fuzz in there also so there may be a bit more to it than that.  There is a very technical description of the classic rangemaster treble booster here that may give some hints --> http://www.geofex.com/Article_Folders/Rangemaster/atboost.pdf

A parametric set with frequency around 60-75%, might get you somewhere.   There is a strong element of fuzz in the tone also so you could try combining it with one of the fuzz distortion effects, using the mix and drive controls  to give a light fuzz.

Use the focus EQ before the amp and miximize the output of the focus EQ. Also set the input impedence to very low 32 or 22 as most treble booster had low impdence. regardin the setting for the Focuse eq try the Low at center and the high full at 100. You want to cut the bass and use the EQ as a high pass filter while boosting the output.