For single stepping you can use a timer connected to NMI. Properly set up it fires just one cycle after RTI allowing the CPU to fetch and consequently execute just one instruction. Within the NMI service you may check the PC against the address you are looking for and skip reporting registers etc. else. This will slow down execution considerably but may be acceptable. And of course you may alter the delay when the timer should fire to skip some instructions or loops.
my 2 cents
6502.org
The 6502 Microprocessor Resource