Land Rover Repair: OEM vs aftermarket, oxygen sensors, reputable service

Question
Hello John,
I have a 1999 Discovery II with 148000 miles with the check engine light, ABS, traction control, and hillside descent lights  on. The engine was misfiring which my local mechanic fixed. I was also told that I need a new catalytic converter( one side is bad) and oxygen sensors.
I am considering doing this work with my son and wondered if this would be a fairly easy repair.  Also is it ok to use "aftermarket" or "replacement" parts instead of OEM?  There is quite a substantial cost savings between the two!
The three amigos I think I will just ignore--is it safe to do this?  Will the brakes operate normally just without the anti-lock feature?  
Thanks in advance for your reply.

Bill

Answer
There is nothing technically difficult about unbolting a catalyst and bolting a ne wone in its place.  From that perspective anyone could do it.  The problem is usually with the six studs where the cat bolts to the manifolds.  If those studs snap you have to drill them out and rethread and fit new ones.  That can be time consuming.

In terms of original vs. aftermarket.  In Massachusetts we have CA emission standards, and the cheap aftermarket cats won't pass that for more than 1-2 years.  In a state without emittion test it might not matter.  These are definititly a "get wha you pay for" proposition.

With respect to your question about ignoring the ABS warning light . . . no reputable service manager would ever advise such a thing! How can I know what's wrong?  If you want some assurance that the vehicle is safe to drive then find a qualified shop with a t4 or autologic test system, have them read the ABS codes, and then ask them if it's safe to ignore.  If they tell you, it's based on knowledge of your truck's real situation.