You can do it yourself if your dampener is degreed or you have a cut-back timing light, but it's a pain, especially if your existing idle is up over 1000rpm and you are in to the mechanical advance already at idle. Most mopar point distributors had 12-13 mechanical advance degrees built in to them ( that would read 24 - 26 degrees at the crank - distributor turns 1/2 crank speed). If you want to set your initial at - lets say 18 crank degrees and you want a total of 36 degrees, you will have to limit the mechanical advance to 18 degrees ( 9 distributor degrees ). To do this you will have to limit the advance travel in the distributor by welding up part of the slot that the pins travel in. You can do it, but a lot of in and out and trial and error to get there - and you still have to address the rate of the curve by ploting it out at maybe every 500 rpm. I'd say find a shop with a distributor machine, give them the parameters you want, and let them have at it. They can also check your distributor for firing point accuracy -warn bushings, bent shaft and your vacuum advance curve if you are using one.