When I did it we used the heater box from the CJ. The only thing borrowed from the YJ was the tub itself. When you use the origanal heater box and duct-work it is nessesary to make modifications to the cowl (the area between the windshield and tub). We cut a two foot section out of the cowl area, where the defrost duct exits into the windsheild. Then we cut the same area off of the YJ tub and weilded the CJ cowl onto the YJs. (Am I making any sence?)
I have never seen anyone use the YJ Heater and duct-work on a CJ conversion. The CJ heater will bolt right up without drilling any new holes in the firewall of the YJ tub. The whole thing is about 1000 times easyer than I thought it would be. I'm Considering doing it agian to a CJ that I bought for parts. It was a lot of fun.
Our project is done now and it lookes sweet. Hopfully I'll be able to post pictures of it some time next week. Ill try to include pictures of the modifications that we had to make to the tub.
1979 CJ7 Renegade 304, 3spd, 2.5 BDS lift, Hedman headers.
Check it out 1979 CJ7