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I would be very hesitant about restoring a firearm that went through a fire. The OP says "antique" Colt SAA but perhaps a serial number would date it better and thus give an idea of just what type of steel it MAY be made of.
One factor to this is that when metals are heated, they can change the molecular structure of the metal itself. Much of this change is affected by the additions to the base metal, (such as the percentage of Carbon), and the temperatures and cooling of the metal after heating. Heat treating of metals is a "controlled" process where metals are generally heated to a certain temperature, then can be quenched in a liquid such as oil, or can have a controlled cooling by lowering the temperature gradually.
Depending upon the process, a metal can be made harder, softer, more brittle, more ductile, or the shape of an object can be changed easier when it is heated. A firearm in a fire that has the grips melted off, and the soldered front sight come off, has definitely been subjected to a high temperature, and uncontrolled cooling after.
A more familiar example of this treatment to alter the molecular structure of a metal is used by Handloaders to alter brass cartridge cases. The heating of the neck area of a cartridge case, and then dumping the heated case in a bucket of water, will soften the neck area of the case, and thus allow it to be worked easier without having the case crack, split or buckle when it is sized. BUT YOU DO NOT HEAT THE WHOLE CASE AS IT WOULD SOFTEN THE CASE TO A POINT THAT IT WOULD WEAKEN IT WHEN FIRED. This is an example of controlled heating and cooling for a specific purpose, with a metal that the composition is known, and is a recognized process.
A firearm that was in a fire has NONE of these CONTROLLED factors.
Although I am not familiar with the exact composition of the metals in a Colt SAA, I do have a fairly good working knowledge of metals. I would suspect that the Barrel is a bit higher grade steel than the frame. The shape of the frame is also a factor, as the cartridge, when fired, will recoil against the frame at the rear. The top strap is a weaker portion of the revolver design, being long and relatively thin compared to the rest of the frame. This part would have heated up and cooled faster, and thus have a bit more distortion as it would have been confined by the colder ends of the frame, until the whole thing heated up. Metals expand and contract when heated, and can distort more or less depending upon it's shape.
Then we have a future scenario. You put this firearm together, and KNOWING it's limitations, you fire low powered black powder loads through it. Then, you die, either naturally or prematurely. The firearm ends up with someone who does not know the history of it, either through sale or inheritance. Your Grandson, wanting to fire Grandpop's old six-shooter, (assuming he will be allowed to own it due to future Gun Laws), buys a box of full powered loads, and goes to try it out. I think we have seen enough pictures of blown up revolvers that we can get the idea.
My own advice would be to keep it as a wall hanger. However, the OP seems to have gathered some parts and seems determined to "restore" it, so this advice will fall upon deaf ears.
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