In their heyday, circle trackers were sleeving the Y to accommodate the 4.00” bore so that part is doable.  As Glen mentioned, the run of the mill Y will not a safely bore out to 4.00” and still have enough cylinder wall remaining to not have problems.  I have seen 312’s that were bored out to 3.925” (+.125” over) but sonic testing of these show them to be marginally on the thin side.  I recently did sonic test a 292 block that would have made a 4.000” bore with cylinder walls that would be thinner than I prefer but probably doable but these blocks are far and few between.

My own perference is to maintain at least 0.100” cylinder wall thickness with any kind of performance use in mind.  Using block fill can allow the cylinder wall thicknesses to be minimized but this also reduces the cooling surface area of the cylinder and subsequently brings other problems to the forefront depending upon the intended use.