I am reparing a 1975 Chrysler 5 HP for my 11 Year Old boy this summer, for little dighny. I have a 5 HP with dead lower unit and a 4.4 with good and an extra l/u. However the 2 extras are long-legged. I can change the driveshaft easily from the bad unit. Can I just unscrew the shift rod and screw the short one down in - or can I see a picture of the internal in this lower unit somewhere online ?