I just went through this tortuous procedure with my 1953 3100 a couple of months ago and as a 'seasoned citizen' absolutely understand your pain. A thick foam pad in floor helps when standing on your head. I made myself a few notes which may or may not help but here they are:
Disconnect battery cables
1) Remove radio speaker panel (4 nuts X 3/8 with washers) This give lots of room to see & reach gauges
2) Remove choke and throttle cables completely.
3) Loosen ignition switch (2 original type screws on bottom of dash)
*PH3 bit-head will work.
* Ignition switch can be carefully moved out of the way without disconnecting wiring.
4) Four 3/8 nuts secure speedometer to dash. Right side are visible & not to difficult.
Left side screws are hard to see & reach, - must feel & remove with 3/8 driver.
5) Remove speedometer cable & 3 electrical bulbs at back of unit.
*3 bulbs are plugged into the back of speedometer unit. A black wire & bulb is the bright/dim and plugs into the top of speedometer. Two white wires with bulbs are for illumination and plug into either side of speedometer.
BTW, I purchased a new speedometer than looks exactly like original except center circle area is a bit darker for $137.00 plus shipping. Might be less expensive than having old speedometer rebuilt.
