i'm upgrading my brakes right now, just wondering if a larger from b series or h series MBC will be compatible with the car, which is still a d series.

 

You can get yourself a 1" ITR MC and BB, but you will have to flare the brake lines

 

Use an 88-91 Civic EX 4dr Master Cylinder which is 15/16". It bolts to the stock Brake Booster, and the lines mount up without any flaring and new fittings. No fabrication of lines at all. If you use an ITR or any other 1" Master Cylinder, then you need the brake booster as well. There are plenty aftermarket remanufactured master cylinders, I got one off of eBay from some Italian brand of auto parts for like $45 or something.