It depends a lot on one's level of skill, if one wants to do all the work.
I recently installed an 8 3/8" barrel with integral sight on a Ruger SA 44 Mag. I wanted a 7 1/2" barrel. Since I had to re-thread it anyway and remove the shroud, I took the length off the back of the barrel. Unfortunately, not an option for you.
Front sight options:
1st: If I was doing your gun I'd search for a 5" barrel on this forum in the classifieds and also on eBay and Gunbroker with equal blue wear to your gun. Sell your barrel to recoup some costs.
2nd: Or buy a 5" barrel front sight/base. After milling or filing a flat spot in the rib at the front of the cut barrel, have the location milled with a mortise (slot) for the tenon sticking off the bottom of the new sight, and have it drilled and pinned in place. Use dome ended pins like older Smiths so you don't have to polish them flat and re-blue barrel. Or cut off the tenon and attach with a screw as in #3 below.
3rd: But if you decide to cut out and re-use original sight; saw out the integral base/sight with a power hacksaw, jig saw, carborundum cutoff disc, hand hacksaw, etc.
Cut into the barrel muzzle horizontally under the sight leaving the top 1/3 of the barrel connected to the bottom of the sight for grinding off later so the saw cut doesn't have t be very accurate.
Cut straight down into the barrel at the back of the ramp to meet your first cut.
Now grind or sand a nice flat surface on the bottom of the sight base, leaving some extra height. After milling or filing a flat spot in the rib at the front of the cut barrel, you can tape sight securely to the barrel and test fire for proper height. It'll be too high so remove metal from the bottom of the base until the POI is dead center at the distance you want, with rear sight adjusted to its middle position. Then you'll have some up and down adjustment for different loads and bullet weights.
If you've decided to use a screw instead of soldering to attach the front sight, it's easier. You can screw the sight in place during test firing. Each time you remove metal from the base of the sight, you can shorten the screw slightly to screw the sight back on tightly.
When you get the height right, grind some grooves in the flat spot on the barrel and the underneath sight base, fill with epoxy and screw sight on permanently. Or install a small pin in barrel with hole in sight base, then glue in place and tighten screw. Then serrate screw head.
I'd use a standard side plate screw 5x44.
Hope that helps your project planning.