hello, i recently seen an article in a bronco driver magazine that told of a heater upgrade for 66 to 77 broncos using a blower motor and squirl cage from a 79 chevy truck. the article had a picture of the stock bronco cage next to the chevy one and the chevy cage is quite a bit bigger. well being the kind of person that i am, i hate it when everybody goes to chevy parts to fix thier ford bronco. so i went the boneyard had to drag myself over to the chevy section and found a 79 chevy truck, pulled the blower motor, measured the squirl cage dia. it is a 6 inch dia cage. i then proceded to high tail it out of the chevy section, and over to the ford trucks where i found a early to mid 90's f250 (92 to be exact)that had been wrecked. i pulled the blower motor out, real easy to get to pass side under the hood, and low and behold the squirl cage measures 6 inches ! so i bought it for $5.00. went home pulled the blower out of my 67 bronco and checked for depth and the are close enough to the same. you then use the newer cage to mark out a line on your heater box for the larger dia. hole, its not much, about a half inch all the way around. i used a high speed digrinder with a flap wheel but you could use a rotory file, dremmel or whatever else you got to make the opening big enough for the new cage to fit in. you want to pay attenion to the bottom half of the heater box because there isnt much material there, it only leaves you with about 1/4 inch around the bottom. while i had it apart i also cut the inlet hole inside the heater box where the air comes into the squirl cage a little bigger. i dont think you have to do this but i figured it might let more air pass through. i then just used some self drilling screws to reatatch the motor to the heater box spliced the wires and ta daaa !!! feels like twice as much hot air flowing through the defrost and floor ducts. the sheetmetal of the newer motor does hang down past the bottom of the heater box a little bit so after i had it mounted i scribed the outline of the bottom of the heater box onto the sheetmetal of the fan pulled it back out and trimmed the extra off using the same high speed grinder with a cutoff wheel. reinstalled it looks as good as it functions. this was a very cheep and pretty easy upgrade to the heater of the old bronco, about two hours start to finish, using FORD parts. none of that chevy crap on my ford. hope this helps somebody out.