Crankshaft end play (float) shims 1956 Dommie 99

Unless you've  replaced your main bearings with rollers, end float on a 56 Dommie is of no concern as the crank is positively located by the timing side ball journal bearing.

I would offer to swap one of the rollers for a ball race that does a better job than the roller. 

I fit the shims behind the inner next to the crank but I only add shims if the endfloat is above 25 thou or there is evidence the crank is touching the cases on one side. For a low powered engine a ball on the timing side works as an alternative.

Fitting double rollers on any Dommie engine smaller than a 650 is waste of time, money and effort unless you are going racing. Two rollers will also add to the internal friction and certainly rob a 500cc engine of useful power. 

There is much to be gained by fitting one good roller and an uprated ball. They make re-assembly much easier and quicker and will almost certainly outlast your ownership of this bike.

On the Timing side go for a a heavy duty ball-race equivalent to the RHP M306. A notched type that employs 10 balls instead of 7 or 8.