I have wanted a Duster since I drooled in the school parking lot at my friend's 340 animal. I just purchased a clean 75, slant-six, automatic and want to put a 340 w/ 4-speed in it.
For those who know, please tell me what to start buying and in what order of priority I need to begin with.

Thanks 4 all help, Hulaagu  

I would guess that if you are replacing the engine and transmission, I would start with that. After that, get all the parts you need to change it over to a manual shift.  

I now what ur saying rolig, 'sometimes you gotta jump in and start at the beginning.' but i would like technical info: what is compatible with what i've already got? s/6 alternator w/340 engine? etc?  

The alternator would work, but you'll need different brackets. The wiring will need to be lengthened in spots, and shortened in others. The radiator MIGHT work, but more than likely, it won't keep the V-8 cool. You'll need the conversion engine mounts from Schumacher Creative Services. There may be more changes needed, but I am not sure what you have, or are trying to reuse.