1993 Mercury Tracer Loud Knocking Noise - Internal Engine

Noises problem
1993 Mercury Tracer 4 cyl Two Wheel Drive Automatic 120K miles

1993 Mercury Tracer 4 Cyl. Engine has approximately 15K miles on a rebuilt engine-No warranty. First thing one morning all of a sudden the engine started making a internal knocking noise. The knocking noise increases as the RPM’s increase. Performance is excellent. The knocking noise has no negative effect on engine performance. It also has a slow water leak. The car was taken to Pep Boys for diagnosis. Their evaluation was: water leak is from a cracked radiator, the knocking noise is coming from the lifters. They can replace the radiator, but they do not repair internal engine problems. They stated that the loud knocking lifter noise is not a major problem and the car can be driven without causing any further damage to the engine. I will have them replace the radiator tomorrow, but it will be another 30 days before I will have the funds to have someone else to fix the lifter noise problem. **My question is, in your professional opinion, do you think that if I drive the car very conservatively 10 to 20 miles a day in big city traffic, trying to avoid exerting any extreme stress on the engine, that it will be OK for about 30 days without causing any further damage. Thanks