You should find the locations for the pipes first so you can work around them with your lug spacing. You don't have to cut them (the pipes) in yet, just know where they're going. . If you're just doing pins and no estrucheons it's something of a lesser concern (you're not taking wood out of there for the estrucheon plate), but it's nice to have a slice of wood between the pipe tab cutout and the cut out for the barrel lugs too. Sometimes things get pretty crowded up around the nose cap area. too.
Are you doing 3 or 4 barrel lugs? (My guess is that with a 36" barrel you'e doing 3.). As a rule of thumb I like to have my forward most lug as close to the nose cap that I still have a reasonable amount of wood left around there to have it still be strong, and things still look balanced (not too crowded). I did my last one about 5" back of the nose cap. As I said, there's a lot going on up there, estrucheon, estrucheon nails, nose cap, wedge, RR pipe. taper of the stock so you can grab the RR, RR, muzzle cap rivet, barrel lug, front sight. All in about. a 6" area.
Why don't you lay it all out on your slab sided blank so you can get a feel for how everything looks all together. After you determine your front lug location it's a simple matter to do the math regarding even spacing between the front lug and the barrel breech to space them evenly.
And of course, look at a bunch of pictures to see how other guys have done it.
