Altitude Problem

I am working on a bathroom where the sewer line configuration worked out so that the street part of the closet bend that is connected to the sewer line, sits about 2.25 inches above the surface of the current concrete floor. I plan on adding height to the floor for an in floor heating system and tiling but the 2.25 inches is still high. The closet bend is 4 inch ABS and I plan on installing a 4 inch plastic closet flange on the street part . The closet bend collar is 1.75 inches deep. I have included pictures.

Can I cut some plastic off the closet flange collar and off the street to reduce the final height of the sitting closet flange. Let's say .75 inches off the closet flange leaving a collar of 1 inch depth? That would give me a final height of 1.5 inches. I can't chip into the concrete floor because the closet bend curves just under the surface - what is exposed is the whole street.

A secondary question is what is the opinion on instead of using a 4 inch closet flange I use a 4 to 3 inch flange and fit it into the 4 inch street.

thanks ahead of time.

I intend on using one of these for a similar situation I will have one day with my cast iron pipe.

http://www.oatey.com/Plumber/Shared/ProductGroupDetail/106/Cast+Iron+Flange+Replacement.html

Slipping a 3" flange into the street would be the way to go then if you needed to reduce the height it could be the street fitting that gets cut. Use enough ABS cement as you do want to make sure if any material gets cut out that it is not compromising a sound fit.
The all ABS flange might not be the most desirable option. One with a stainless steel ring for the toilet to secure to would be preferred for longevity.

bend

Cut the spigot off even with the floor. They normally have a very long spigot part, but if yours is to short for the outside flange, then the inside is going to be too short for an inside one also.