No known mechanical modification for the T-85 tranny, Mark.
Driving option: double clutch when down shifting IF you're not coming to a stop . . . ?
Ford offered some all syncro three speeds in later years . . . I suspect that they were used behind small cubic inch engines and do not have the strength to withstand y-block torque. Perhaps others know the specifics on these.
For improved driveability, consider looking at installing a four or five speed transmission.
The Borg Warner T-10 (T-85 predecessor) from an early Mustang is probably the easiest bolt in for a little 'Bird. The Ford
Top Loader can be made to fit behind a y-block also. -Front bearing retainer diameter reduction, and possible input shaft length modification.
Personally, I'm working through a Tremec T-5 installation. IF you Google
'Moder Driveline', toggle
'Tech Alley' and then select
'T-5 History', they have an interesting overview of the evolution of the T-5. The T-5Z has a torque rating of 330 ft. lbs. -sufficient for most y-block builds.
Modern offers the Tremec standard .63 overdrive ratio for 5th gear and offers an optional .73 or .59 ratio as well. Installing a T-5 behind a y-block will require a bellhousing adapter, and different pressure plate, clutch disc, and throw-out bearing. John Mummert's offerings can make these installation details easily accomplished!
Hope this helps!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York