After my 1986 6 speed debacle, I shudder to venture a guess.

There is an old BF thread from 2009 where the OP stated the rear dropout spacing for a 1985 MB-2 is 130mm.

It would be a reasonable assumption that if the 1985 rear dropouts would accommodate a 6 speed freewheel that Bridgestone would not make a frame design change of the rear dropout width to run a 5 speed. I cannot imagine the 1986 rear dropouts being 120mm.

If the rear dropout width is 130mm, or even 126mm, you should be able to run a 6 or 7 speed freewheel. The are “generally” interchangeable.

You might have to swap a spacer from the NDS to DS and re-dish the wheel. I don’t know if the wheel is setup so the 1st cog of the 5 speed freewheel is a normal distance from the DS dropout, or further inboard.

Since 6 and 7 speed freewheels are wider and the DS bearing is inboard, there needs to be enough spacing so the axle locknut clears the freewheel width.

John