When it comes to games like Swords & Wizardry, or even BFRPG, I prefer using the d6 skill system to resolve issues like Thievery or Climbing up a tower. That is you have a skill, let's say Climbing (1) for your first level Thief. When a Thief wants to climb a sheer wall they roll their d6 and aim for a 1. This means they roughly have a 16% chance to success. Now this chance can be increased through equipment. An interesting question is could attributes effect the die roll? I believe they can and I have these ideas.
First Step: Assign an attribute to a skill. Climbing takes a great deal of Strength, so one might write down as Climbing (Strength)
On a 14 Attribute: Add +1 to skill roll. A skill cannot go higher than 6, however, a character can now re-roll a failed skill roll at a rate of 1/day. This many uses per day may increase at GM's discretion.
On an 18 attribute: Add +1 to skill roll. A skill cannot go higher than six, however, a character now rolls 2d6 and takes the better of the two results.