According to Doug Turnbull(Turnbull Restorations), First Generation Colts were initially made with iron frames, then colour case-hardened. The cylinder base pin was retained by a screw on the front of the frame.
In Jerry Kuhnhausens's Shop Manual, it mentions that up to around SN 96,000(1883)Colt cylinders and frames were made from metal resembling high grade malleable iron. From SN 96,000 to around 180,000(1898), cylinders/frames were made from low carbon steel. After 1898, Colt used medium carbon steel. Colt did not certify their revolvers safe for use with smokeless powder, until 1900....when the company started using an improved method of heat treating their frames.
So, what all this means is that, your 1880's-vintage Colt should likely only be fired with bp rounds. And only after being checked over thoroughly, by a competent gunsmith. The bp cartridge loads you found should be safe for use. But...only if your gun is in good mechanical condition. Even then, light loads would still be prudent....as Fingers284 suggests.
Trail Boss powder has been suggested as an alternative. Before even considering this powder as an option, take a look at the sharp pressure spike produced by it, upon firing. This powder may be safe to use in modern steel revolver frames. But may not be considered safe to use in any iron-framed revolver. Nor any other smokeless powder. Considering the metallurgy of the time and number of years this revolver has seen....this option would need careful consideration. Even then, only after being passed as safe for use, by a gunsmith. Food for thought.
You could try asking the folks on the "cast boolits" forum, for their advice on which way to proceed. Likewise, Peter(Rusty Wood) would be an excellent choice.
Have you considered reloading as an option? The .45 Colt is a very easy cartridge to load, using black powder. A simple, single stage press, plus a few other reloading accessories is all that you'd need. Brass, bullets, powder and primers for reloading the cartridge are readily available. Since you're in Sarnia, you could try "The Frontiersman" gun shop...116 East St., Sarnia. Then, there's Gators, in Wyoming. If these shops don't stock black powder....Hummason(near Ancaster), generally has a good supply of Goex black powder on hand. Plus lead bullets(DRG), and primers. You can buy new brass just about anywhere.
Hope this helps.