Culturing the Westy 12 yeast would always be a plus..
Westvleteren gets their yeast from Westmalle, which is easier to get your hands on as a yeast source. Even easier is Wyeast 3787 or WLP 530, both of which come from cultures originally harvested at Westmalle.
As for your grain bill, the following info comes from
Brew Like A Monk: it's made to an OG of 1.090 (though the original recipe from the 1930s was 1.120, 12 degrees Belgian, hence the name, they've reduced it since then), 40 SRM (a bit darker than your proposed recipe), and 38 IBU (a little less than yours, but a comparable BU:GU ratio).
About the Westvleteren 8, which is also a dark beer but not quite as intense as the 12, he says that the only malts are pilsener and pale, with sucrose and caramelized sugar adjuncts (in other words, all of the color comes from candi sugar, albeit in liquid rather than solid form). In this, it matches your recipe quite well, though you'll want to consider more or darker candi sugar, though some of the color may also come from a longer boil (your 120m will get it a bit darker than the stated 33). I would also add white sugar to lighten the body and produce a certain vinous aroma. Most strong Trappist beers are about 20% sugar adjuncts total; I'm going to guess that yours comes out with a heavier body than the real product. (Your quoted attenuation is low, at least - Westvleteren 12 reportedly gets an apparent attenuation of 86%.)
Your hop schedule is probably fairly close to correct, though you'll want to scale back unless you want a hoppier beer than the monks brew.
Because of how much the yeast contributes to the character of a good Trappist-inspired beer, you'll want to pay careful attention to the temperature schedule. Westvleren pitches their yeast at 68F, but allows it to rise over 80 over the course of their primary fermentation (which is less than a week long). Secondary is at 50F, until it drops clear (typically 8-10 weeks). They bottle condition for 12 days at 79F. When I do my own trappist-styled beers I'm aiming closer to the Achel fermentation schedule of one week at 75-80F (which I get by brewing in the warmest room in the house) and two weeks at about 30F (a dedicated minifridge dialed down that cold); I suspect that chilling your wort more than I do and then doing primary in a warm room will let you mimic the rising temperature primary of the Westvleteren.
Have you tried W12 and your clone side by side? How did they stack up?
but i have a recipe in mind for trying it out based on how ive heard other ppl say it tasted and other clones ive seen also if it could be in extract form or PM would be good i usually do a bit of PMing in my beer so thats cool thanks
