you can also look at the darts dusters with the 4 speeds they will be od though but that may help you if you wanted overdrive . or as mentioned you can get a 727,but the only thing with that is there is no OD
A518 could work it comes in quite a few dodge trucks Daks,vans etc 4th has a big OD ratio i think its .68 i could be wrong though.but it something like that
The 518 is basically a 727 with with an elec. OD on the end of it
heres more info on the swap:http://www.transmissioncenter.net/SwapInformation.htm
kickdown http://www.bouchillonperformance.com/BPEtkdc.asp