Ayuh,..... You need the proper gasket under the housing, with the brass rivets, to ground the housing, so the sender can tell the gauge where to point too,.....
Ayuh,...... Welcome Aboard,..... Don't use poplar, as it rots quicker than birch when/ if wet,......
As noted, use acx or bcx which is SPF, Spruce, Pine, or Fir based,.....
Ayuh,..... Welcome Aboard,..... So what motor, 'n drive are in yer boat,.....
Trim/ tilt is related to the motor, so diagrams are probably available,....
Ayuh,..... Welcome Aboard,...... As noted, you need a new lower shift cable,.....
Unless it's just been done, All of the rubber parts in yer transom assembly should be replaced, along with the cable,.....
Ayuh,..... Welcome Aboard,..... There is no automotive cap for that distributor,.....
It's a Merc marine distributor,....
Automotive plug wires don't work either,..... too short,....
Ayuh,..... 'n if that ole heavy starter is in fact worn out,.....
Toss it overboard, 'n get yerself a pmmotor starter, with new bolts For it,....
'bout 1/2 the weight, 'n nearly twice the power,.....
Money well spent,....