6* initial is pretty low for an FE.
For learning I'll explain timing a bit. Everything assumes your timing marks and balancer reflect true TDC with #1 cylinder.
There are three kinds of timing. Initial or static, mechanical, and vacuum advance.
The initial and mechanical add together to make "total timing". The extra vacuum advance timing is NOT part of the total timing but does come into play for tuning and efficiency so it must be address correctly.
"Initial timing" is what you change when you turn the distributor in the engine. This is also the timing most know from reading a book because everything else just happens inside the distributor. This is best set with a timing light.
"Mechanical advance" happens within the distributor and is controlled by springs, weights, cams and limiters (posts, bushings, slots)
The mechanical timing requires some spinning of the distributor shaft in order to impart forces on the equipment controlling the timing and plate movements. This is best set with a timing light.
You must get into the internals of the distributor in order to modify the mechanical timing. There are a few screws, clips and roll pins that hold everything together. When removed you can take things apart to get inside and make adjustments.
Some distributors have everything right there under the cap (MSD) while others take a bit of dismantling, none of this is very difficult. Be careful to not lose the tiny parts or bend things. Inside you will find cams, reluctor arms with slots, posts and springs. The slots and posts limit full travel of the advance mechanism while the springs control when, at what rpm, the advance happens.
Last is "vacuum advance" This is controlled by the vacuum signal, diaphragm adjustment, lever arm, plate movement.
Setting proper timing for your specific engine needs is job number one in terms of tuning. If you do not have a good advance curve and timing, everything else you tune will be based off a poor foundation.
First thing to find is total timing and when it happens. This is done with the vacuum advance removed and plugged so there are no air leaks. Having the engine up to temp is helpful too but not required. With the timing light hooked to #1 plug wire read the timing on the balancer. As you raise the rpm of the engine the timing mark should smoothly increase in number. At some point while increasing rpm the timing will cease to raise. This is your total timing rpm as well as total timing of the distributor with regard to how it is currently set up. Let the engine return to idle and read the marks at idle. This reading at idle is your initial timing. Adding the initial and mechanical timing together gets you your total timing. If you know total and initial you can find mechanical with subtraction methods. For instance total is 35* and initial is 6*... 35-6=29. This means your distributor is set up to deliver 29* mechanical timing and the rpm at which this first occurred is also your total timing rpm. Creep up on this total rpm to best find the real speed. It is easy to rev more than needed because once the springs and limiters are overcome by rpm forces timing stops changing. This means your total rpm could be 2800 rpm but you revved to 3100 rpm and did not notice the difference. That difference is important so carefully find it. Once you know total you can then begin playing with initial as well as the advance curve (at what rpm things happen)
To adjust the total limits you must play with the mechanical limiters. This can be accomplished by changing bushings, bending tabs, opening slots with a file or welding slots closed to custom make a certain size opening. None of this is difficult but does require trial and error so you may be doing the job a few times before getting it just right. Do the math and things go quicker.
Adjusting rpm when things happen requires spring changes. Stiffer for later/slower timing and lighter for earlier/faster timing. You can also have different spring rates on each post to tune even more. These adjustments are made to get the right combination between initial and mechanical advance to arrive at the correct total timing. For instance, your 6* initial and 29* mechanical gives a 35* total. A 15* initial with your 29* mechanical would result in a 44* total. With the 15* initial you would limit the mechanical to 20* to arrive at the 35* total from above.
Setting the vacuum advance requires loading your vehicle and test driving to determine best setting. We will leave that alone for now.
For most FE's running factory style iron heads it seems 35* total works very well. FE's also seem to like more initial advance and settings in the 14-18* range seem to be pretty useful. If you are running aluminum heads you can experiment with higher total timing in the 36*-40* area.
I suggest you try 15* initial and 20* mechanical for a total of 35* as a good starting place.
The total advance rpm will depend on a few things, vehicle weight, gear ratio, tire diameter and traction, cam specs and a few other things.
I suggest you try to have your total "all in" between 2800-3300rpm for starters.
If your mechanic does not understand these concepts I strongly suggest you seek a better mechanic.
I hope this helps you get going. Proper timing WILL make or break (literally) a good engine.
There are many factors effecting the exact best timing settings but this should get you pretty close.
