904 Conversion to 727 in early a-body?

Is it a slant 6 tranny you've got now? You can find the numbers on the drivers side of the tranny. I don't think the slant 6 one will bolt to a V8 though.

A-904-G = slant 6
A-904-LA = V8

Why not get a later style 904 (same as a 904 with a different number) like an A-500 or A-518 or A-998 or A-999. I don't know all the ins and outs of installing one of these, or how to convert them to the cable shift, but I have read lots of stories of people successfully using them in this way.