1987 Volvo 245 Torque convertor question

Transmission problem
1987 Volvo 245 4 cyl Two Wheel Drive Automatic 171K miles

I have the above car, got a good used aw70/71 trans from a '90 Volvo 760 as written on trans housing. It is a lock-up unit with a 6 cyl torque convertor. I would like to know if I can get a 4 cyl lock convertor to fit on this trans. I was told at a torque convertor builder that I cannot do that. I've spent way to much moolah on this vehicle and can't stop now within 2 months of usage. As far as I can see on the used trans, everything is the same and will fit, but the pilot dia. Is different on the 6 cyl convertor which I don't care if it is changed to a 4 bolt 4 cyl lock up convertor. I don't care if the lock up works or not, this trans is very clean inside when the pan was drop and inspected. If you can come up with a correct convertor, give me the part number or whatever. Most appreciated. Fred. 5.30.09