Well, if the parts are on order you either have a clearance issue or you don't.
lp231 gave you two ways to go if you can cancel the order. You haven't told us the rest of your specs and plans, but we can still predict the lack of memory heatsinks won't affect your rig's performance.
If you're committed to the order and wind up with a clearance issue, you can also bend or alter parts of the heatsink(s) to create clearance. Since they don't affect performance . . .