Gun builds take time when you have specific design criteria. Common gun build parts like you are talking about here means there are more options, but a lot more people doing the same thing. Be patient, get the critical parts (like the barrel) when they become available. Some times, it pays to contact the distributor and see if you can get on a waiting list for the part.

A stock change for this build may very well be a requirement. It's just part of the gun build decision making process.

My last gun build (a 308) took me about 6 months, and I basically got all the parts from one location at the same time. Custom builds take time and money, some more so than others.