411 from the interweb:



"The 200-4R overdrive trans has a 27-spline TH-350-style output shaft and is commonly found in ’81-’90 Chevy Monte Carlos, Malibus, El Caminos and Impalas. These transmissions are durable enough to withstand the punishment of the legendary turbo Buick Grand National from the factory. The 200-4R measures 27.75 inches, with a 26.81-inch mount position. To swap with the ’Glide, the crossmember must be moved back 6 inches. The good news is that the driveshaft will not have to be shortened."

http://www.drwtransmission.com/thm_200-4r.htm