A word about engraving: for value appreciation I always choose factory engraving. The level of engraving doesn't matter, choose what you can afford and future value will appreciate proportionately to what you spend initially. After market engraving can be iffy for appreciation and may actually de-value the gun. It must be from a known master with certification to have any potential for future appreciation and resale demand.
This will give you some guidance on the nuances of the 3rd gens.
Most Colt SAs do not have an accuracy problem, it's just that the point of impact is not always at the point of aim. That can be adjusted however. Here's a general guide to the 3rd gen Colts which have the greatest quality variances compared to the 1st and 2nd gen single actions.
The SA46XXX to SA05XXX range 1981-86, is about the peak of the worst period. I'll try to put a bracket on it: The very early 3rds with an SA suffix are fine and compare well to late 2nd gens in quality if not features like the trigger guard bevel, cyl base pin bushing, et.al.
Starting about 1980 # SA3XXXX range thru about 1989 #SA94XXX, inspect very closely for:
Cyl end shake (fore and aft play), flattened hammer spurs, off center firing pins in the hammer, bad backstrap to hammer base flush fitting, crooked front sights, sloppy actions with more than four clicks, crooked rolled stampings on frame and barrel (sometimes patent dates are missing altogether), lousy case coloring, poor grip strap to frame fit, over polished edges or edges so sharp you could cut yourself, etc., etc. The labor strike was in 1986. Now having said all that, I have found an occasional decent gun in that period.
After that period things start to improve with typically only one of those problems per gun but sometimes more, and sometimes none. The lousy backstrap 'ears' to hammer base fitting is still fairly common as are flattened hammer spurs. Once the SA in the serial number splits SXXXXXA in 1993, they continue to get better thru 1999.
At #S26XXXA in 1999 the authentic removable base pin cyl bushing like 1st and 2nd gen guns is re-introduced and cyl end shake is all but eliminated. Case colors really improve as well as fitting. Hammer spurs are correct as well as most backstrap ears to hammer base fit. Now the guns are approaching late 2nd gen quality and do to this day. However the trigger guard/front grip strap still does not have the bevel of the early 3rds with SA suffix or wide loading gates of the early 2nd gens and probably never will again. The 2nds never had the 2 line short barrel address or 1/2" radius flutes of the 1st gen, and even the late 1st gens lost the case colored hammers and all vestiges of the front cyl chamfer. At least three pre c. 1936 features can be special ordered now on 3rd gens; CCH hammer, the 2 line barrel address on short barrels and the cyl chamfer, but it's not accurately done. Of course there's a one year plus wait.