New Member with a big question

The estimate on the motor is 800-1000. The estimate on the transmission is 2000-2500.
Those figures look backward to me.
Every high milage engine that got water or gas in the oil didn't live very long with just fault corrected. The sediment gets washed out of the main bearings and rod bearings causing them to fail.
If a linkage adjustment cured the trans issue, thats all good for now.
You have a 73 340 which is somewhat rare so spend whatever it takes to rebuild that engine before it self destructs.
The transmissions are all too common and easy to replace.