Well, I am finally getting around to this upgrade.  I figured since the engine is out, and I have most other "issues" taken care of, that I would pull the dash and re-wire it and in the process of it being out, take care of this upgrade that I have been wanting to do for many years now.

This upgrade will give you a higher volume of air from your defroster and heater.  Since this is a larger blower motor, it will spin your fan faster, giving you more air out of the heater box.  This is well worth the little bit of money and above average labor that it takes to do it.

This upgrade works for '78-'86 CJ's as well as the '87-'90 YJ's.  Some of the CJ's built in 1977 used the old style heater housing with the heater motor behind the dash.  I haven't heard of anyone doing this upgrade with the old style heater housing or with a Wrangler built after 1990.  Any 1977 CJ with a heater motor sticking out of the fire wall will be able to do this upgrade.

HEATER MOTOR

You can purchase this motor brand new at most auto parts stores for under $30, so it's really not worth the time to search a junkyard for this part.  And with the labor involved with putting this in, I didn't feel like tearing apart my dash and heating assembly in a year just because that junkyard part was on it's last legs.

When you go to your local auto parts store, you want to ask for a heater blower motor from a 1973 Chevy Blazer with a 350 and air conditioning.  The part is the same for all blazers of that year, but you don't want to confuse the idiot anymore than necessary.  The actual box has "Factory Air" on it with the part number 35587.

Advance Auto Parts -- PN: 5012066 - $20.99

If you do decide to hit the boneyard for the motor.  The actual motor was used over several years in several different models.  I don't have a complete part cross reference, but any motor out of a Chevy pickup, GM pickup, Blazer, or Jimmy should work from '71 to '76.  The motor may have the part number "1312" on it.  The new one I purchased even had that number on it also.

Here you see the new blower motor next to the stock CJ one. You can see the size difference and how the portion that sticks out of the firewall into the engine bay is larger in diameter, the need for the larger hole in the firewall.

INSTALLING THE MOTOR

The only tricky part about putting this in is that you have to enlarge the opening in the fire wall for the motor to 3 1/4".  A air cut off wheel, drill with a hole saw, saber saw, or hack saw could be used to do the job.  Other than that its just a matter of unbolting the heater box and unscrewing the old motor, if you have changed your oil by yourself, then you can do this mod.

First thing you want to do is drain about 1/4 of the coolant from your radiator.  It might be a good time to put in some fresh coolant or even flush your system.  If so, check with your local laws on how to properly dispose of your coolant.  Do NOT pour it in a storm sewer.  For most animals, drinking coolant causes kidney failure, so if you really want to get rid of that damn cat, well, you didn't hear it here.  Be sure to "burp" the system when you refill the coolant to get all the air out.

You also might have to remove your battery tray to make things easier, mine is out anyways so I can't quite tell for sure how much of a pain it would be. 

Disconnect the two hoses on the engine side of the fire wall that go into the heater core.  There should be a wire connection there also, disconnect it.  Also remove the drain hose that drains the bottom of the heater.

This is another area that is grey for me.  I took out my dash to work on it, but I'm sure you could get by with just taking out the bolts and pulling it out a little to get at the heater box.  Or if you are a contortionist you can just take it out and not touch the dash.  So, now that you are under there, unhook the heater control cables and the wires that attach to the heater box behind the dashboard.  Also disconnect the defroster duct hose at the top of the heater box.

Remove the four nuts that secure the heater box on the engine side of the fire wall.  Three of them are pretty obvious near the heater hoses and heater motor, the other is near the middle of the fire wall behind the valve cover if you have a 258.

After you get these nuts off, you can wrestle the housing out of the Jeep.  Once it's out you just unscrew the motor in the back side of it.  You might have to pry it out, since there is probably some caulking around it.  Now unbolt the fan and bolt it onto your new motor and replace it in the heater box.

Here is the new blower motor in the CJ heater box.

Now all you have to do is to enlarge the hole in the fire wall.  Like said above there are several different tools you can use and several different ways you can do this.  I lucked out and used a plasma cutter.  Yep, lucky me.

I put the new blower motor in place and marked it.

Here you see how much larger over stock the new hole will be.

Once you have the hole done you just have to reverse the steps and install everything.  And keep in mind you will not be able to reuse your rubber seal for the blower motor.  All I did was to use blue silicon RTV, it's just there to keep water out.

Thank you Neil for the pictures!