3spd to 4spd OD trans

I've read about 23 different posts about the OD tranny's. I'm still a little confused:?: ......... some of the questions I had were answered and some left me still wondering so I'm going to see if I can get a more specific answer if possilbe on some of my concerns.
First **
I've got a 904 trans behind my 340 tucked inside of a 73 Duster using a positraction unit with 3.55 gears......mostly to be used for crusing but an ocassional rubber burner:burnout:
I'm using this tranny with a 'B&M star shifter'. I'm wanting to put in an A500, since it seems to be (from my reading) a lot less of a problem than the A518.
Some say that you have to make the tranny tunnel a little larger to accomadate the switch over...........?? IS this true for a 73 Duster??

Second **
I currently have a 3000 stall converter in the 904 and when I change over to the A500, can this converter still be used or what will I have to do to utilize the stall factor of the A500 or is it not needed??

Thirdly **
I've received information about an A500 w/converter that has the 8 pin connector ........... said to have 23,000 miles. It 'supposed' to have come out of a 1999 1/2 ton dodge ram (2 wheel drive) that had a 318 engine (this unit being offered to me for sale ($250 + shipping)....good deal or not, I don't know.

Fourth **
I had found somewhere a wiring diagram for the A500 but NOW can't seem to find it.......any help on this will be very helpful.

Fifth **
I realize (from reading here) I'll have to shorten the driveshaft and modify the transmission Xmember..... other than that, I think that might be all that I'm really aware of.

I'd appreciate any help on this conversion........with the cost of gas & my current gas milage, I'd like to improve the milage so it won't hurt as bad when I go to fill up.

Thanks in advance...........:thumbup:
Greg