Please note the question is more or less an offtopic for this forum. There are basically three sources mentioning the reorg, and they are somewhat differ from each other:
1. Феськов В.И., Калашников К.А., Голиков В.И. Советская Армия в годы "холодной войны" (1945-1991).
2. Дроговоз И.Г. Танковый меч страны советов.
3. Ленский А.Г., Цыбин М.М. Советские сухопутные войска в последний год Союза СССР.
Combining them, the version looks as following.
Reorganised carried out in 1984. No data available on reorg end. Full name is "5th Independent Guards Army Rogachev Red Banner Suvorov's and Kutusov's Orders' Corps named after Supreme Council of Belorussian Soviet Republic".
Reorganisation looked like:
355 Gds Tk Rgt -> 1 Gds Tk Bde
339 Gds Mot Rfl Rgt -> 2 Gds Tk Bde
334 Gds Mot Rfl Rgt -> 177 Gds Mech Bde
356 Mot Rfl Rgt -> 176 Mech Bde
276 Helo Rgt, 1318 Descent-Assault Rgt and 1180 Ind Rocket Bn were added.
310 Gds Art Rgt and 1045 Gds AA Missile Rgt remained unchanged and were included into the Corps.
Also remained unchanged and included into the Corps were 7 independent battalions, supposedly: 46 Ind Recon Bn, 126 Ind Gds Engineer-Sapper Bn, 149 Gds Ind Signal Bn, 73 Ind Chemical Defense Bn, 1626 Ind Supply Bn, 82 Ind Repair&Recovery Bn, and 274 Ind Medical Bn.
Reorganised back to 120 Gds Mot Rfl Div in late 1980s.
