I don't quite get what you mean by .50 tall - that is a full half-inch and is a massive adjustment in a front sight.
The No 4 sight elements all have the same blade height - about .145".
It is the height of the base block which varies. The sight bases are marked depending upon how their base thickness varies from the standard size.
On a No 4, the "0" marked sight is designed to put the top of the blade 1" above the centre-line of the bore. Sights varied in increments of 0.015".
If you in fact need to increase your sight height by .050", you could go up three sizes (.045"), so -0.015 + .045 = .030" would probably be the one you want.