Is it a relatively simple matter to transform a 44 Mag to a 45 Colt? Would the reboring of the cylinder & barrel be a pretty straightforward modification?

Yes fairly straight forward for a 'smith that knows what they are doing. A rebore will run you about ?
$175 and take at least six months to get done. The rechamber around $150 or so. Remainder of the work $50 or so. Shipping excluded. Would be much easier to sell and buy though you have one of the finest I Houston that could do the work if he was interested. I am sure he would have a take off barrel that could save some money. Alan Harton.

EdM nailed it. Alan is the best in these parts, if not anywhere. I had him do this exact thing on a old model 3-screw Ruger SBH a couple of years ago, and I did have him use a new take off .45 barrel for the job. I can't recall the exact costs for that work specifically as I had him do a lot of other things as well, like fit a Colt 2 pc grip frame to the Ruger main frame, and he had some pre-ban ivory one piece grips made for it as well, did a high polish bluing job to boot. Alan will take anywhere from a few months to a couple of years depending on his work load though. Perfection is in high demand! He can make you a "tight" 45 Colt out of that 44 mag cylinder that be tighter than before and make your brass go further since it won't work around as much in the chambers.

Reason I ask, there are so many more formats, both single & double action, available in 44 Magnum. I look at them and think it would be nice if the same were offered in 45 Colt. Several of the S&W's would be wonderful in 45 Colt. But, they just don't offer them.

Haven't heard of Alan Harton. I'll have to look him up.