Well sorry Gary, I think we are all just sugesting other options to look at, since most of us do not like the BW35 very much. After all, your question was :
What's the general opinion on the feasibility of replacing the BW-35 automatic?

If you want automatice ánd save money, the BW35 is the way to go. But since you already figured that out and don't want to hear about options, why ask?
Anyway, its easy to swap one BW for an other. There should be no problem with kickdown cable or shifter linkages or whatever. The only thing you might run into, is the fact that some BW35 are longer then others, which might require shortening/lengthening the drive shaft. Hope this helps.

Cheers
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)