The scope of the jam is basically anything that could've existed between 1974 and 1987. (You could argue 1982 because Dragons of Despair was released that year, but I am going with the release of the DL sourcebook. I do not agree with the jam that DL somehow ruined D&D. I loved my Minotaur Cleric.)
Farrago is based on someone trying to mix AD&D with various d100 games that were around in the 80s. Yes, this is something I would have done.
In game play, Zoran's character sheet will already show the lockpicking skill as 84. When attempting the pick the lock, the player will simply need to add 10 to determine the upper target number. The ajudicator may simply state the lower target number instead of stating the difficulty level of the lock.
The players may also use any means to lower the difficulty level of the lock through others means such as magic, knowledge of locks, or brute force.
For example, Zoran is a character with an Agility of 16, a lockpicking skill level of 4, and a magical charm that adds 10%. When Zoran attempts to pick the lock, the upper target number is 16 (AGI) * 4 plus 10. This provides an upper target number of 94.
The adjudicator determines that the lock has a difficulty level of 5. This makes the lower target number 50. Zoran must roll between 50 and 94 inclusive to pick the lock.
Farrago update - The core mechanic:
In situations with a chance for success or failure, the player will roll d% between a lower target number and an upper target number. The upper target number is determined by the appropriate stat multiplied by a character's skill level plus modifiers based on circumstances, equipment, and/or luck. The lower target number is determined by a difficulty level set by the adjudicator multiplied by 10.
Call me Bear