a 27 is a 27 and a 28 is a 28. Never the twain shall meet.
I have a 3 1/2" 27 and it is a wonderful gun. I also have a 4" 28 that shoots just as well.
Years ago when 28s were cheap, many were used as a base for some really nice custom guns. But the value of 28s has jumped considerably since then. Cutting the barrel on one would cost you money and in the end you'd end up with a gun worth considerably less than the original.
Just save up your money and buy a real 3 1/2" 27.

But since we're on the subject of custom Model 28s.....
Some years ago I came across a bare nekkid Model 28-2 frame cheap. It took about two years to get all the parts together and then a good bit of work on my part, but I put together a custom Model 28 snubby in .45 Colt. I like it!