Well I have no experience with Yohimbe (it's banned in Canada I believe) but I have done an ECA stack.

I started with:

1 - ephedrine (2.5mg.. I think)
1 - caffeine (125mg... I think)
1 - aspirin

And I worked up to 3 ephedrine with the 1 C and 1 A. That stack was a bit of an ass kicker so I would be reluctant to throw in a Yohimbe on top of that.

I also would recommend the asprin as it has a blood thinning/ blood pressure decreasing effect.

Maybe you could start with the ECA and add in the Y after. Have you ever done a stack like this before? Do you drink much coffee or energy drinks?

Also... how much is a stone...? lol I think it's like 13lb or so but I can't remember. So 1.5 stone would be about 20lb... That's alot for a month but it is doable. You will want to set out a meal plan with a deficit of at least 500cals and you'll also want to be doing cardio as much as you can. Keep your lean protein as high as you can and what carbs you consume should be whole grain/whole wheat and what fats you consume should be good fats... aka olive oil, peanut butter, almonds. Etc. Also, heavy on the veggies and light on the fruit.