Last night I started the heater fan replacement project in my 1974 145 and thought I'd pass along the procedure I followed, before I forget. It went a little more methodically this than last time.

REMOVE THE DRIVERS SEAT! Removal made it much easier to get at both sides of the heater box, and I was able to work inside the car entirely during the winter.
Other preliminaries: disconnect battery, don't drain coolant.

-Remove console side panels and loosen fron panel.
-Unscrew steel console frame from floor, pulling back carpet.
-Unscrew steel console frame from knee level cross members.
-Pull the console fram forward an inch or two.
-Unscrew lower plastic ducts from floor, pull them slightly away from floor to break glue.
-Unscrew and remove kneepad on passenger side.
-Unscrew and remove steel cross member from passenger side.
-Remove glovebox. Use stubby phillips to remove 2 screws inside upper front edge.
-Reach around back to press glovebox door supports inward to clear glovebox and front frame. Lift door off and pull glovebox out from back.

-Remove all little metal clips from the rim around the heater
-Pull on upper air duct away from heater box, breaking the sealant between box and duct. Someone said there are 2x10mm mounting bolts hidden in there somewhere but I didn't find them.
-As you pull on these ducts, you just want to give yourself some wiggle room. You will have to wiggle the covers off. They are somewhat fragile, adn will crack if you yank on them. They are fiberglass, not ABS plastic.
-Pull lower duct away from heater box to give a little wiggle room.

-As the passenger side cover comes off, make note of the lower flap placement. The passenger cover should come off pretty easily.
-Slip a fine blade in to crack the cases. They are not glued OEM.

-The driver cover somes off with more difficulty. The knee-level steel crossmember is connected to the steering column and interferes with the cover.
Pull back both upper and lower ducts as much as possible, and work the loosened cover around until it slips out between the crossmember and heater case. It is tight, but can be done. This is where removal the drivers seat makes complete sense. You may want also want a pillow in there somewhere. No sense in being uncomfortable.
-Remove the fans by prising the little clip off. MARK THEM LEFT AND RIGHT.
-Remove the inner fan casing on the drivers side. There are three screws, maybe 4.
-Remove the motor mouting support, 3 screws.
-Cut the wires and pull the motor.
-Sit on your pillow and stare at it for minute.

As they say in the Haynes "Replacement is a reverse of removal"

I have the new motor, which apparently has different wiring, and requires a change of the heater switch and a resistor, but that is easy compared the this job so far.

-The new motors have a wider case, so you have to grind away some of the sides of the mounting hole throughthe heater box. I used a 2 inch drum sander. Vacuum up the dust, you don't want to breath that.
-Put the motor in from the drivers side, wires first. It's easier to fee the wires up through the top from the driver's side also.
-Feed the wires up through the top grommet, and pull the ends down far enough to get at.
-Replace the three screws through the motor flange.
-Replace the inner left cover.

-2 hours so far.

-Put the fans on.
-TEST THE MOTOR.
-Replace the covers, lining up the diverter flaps.
-Test all the vacuum connections, look it all over.
-Replace all the stuff.
-Take some minor exhausted satisfaction from this, the most awkward, seemingly trivial repair, and then try to forget the whole thing.