I can't imagine how many 35-37 Packard transmissions there are still left in captivity
but it's unlikely it would be a bolt in. Things to consider would be having the clutch gear
the same length and have the same spline as your existing clutch. Would the mounting
for the transmission to the bellhousing be similar. Also what type of output shaft would be
needed. What other fabrication and or machining would be involved. It sounds like a lot
of work and expense for minimal gain.
Fred