Thomas wish I could help but I am strickly a wide frame 1X8/9 guy, but someone will get you soon,,,
If you go to the bottom of the topics page there is a manual section. When I looked at page 20 of the chassis section (i believe you said an original)it only talks about 4 cap screws probaly 9/16 or 5/8
But I am out of my knowledge zone with narrow frames...