If I recall I put stops in the accumulators to reduce their volume. Higher spring rate slows the clamping. Higher preload delays the shift. By shortening the travel makes a quicker shift.
Since these are a sequential shift transmission meaning each upshift just locks an element the timing is not critical so a soft spring and lower volume will firm up and quicken the shift. There are restrictor in each fluid passage to the accumulator, these get opened up a bit. I leave the check valve in.

The Toyota Cressida had an electronic trans at that time. I expect it would provide the valve body and such. I do not have hands on of that period Volvo autos.