In theory, the answer is yes. A .50 cal supressor would/could be effective when used on a .45 cal weapon. However, I would double check with the manufacturer to make sure. Do you know for sure that it is a 50 BMG can and not a 50 S & W can? Some cans that are made specifically for handgun bullets will not hold up well at rifle pressures. The most common examples would be the purchase of a 9mm (.355) can and then using it on a 300 RUM (.308); or a .22 cal supressor made for rimfire pistol or rifle and then using it on a 5.56 Nato rifle. Quite often, cans made for pistol calibers end up costing less than the rifle counterpart and provide a tempting low-cost alternative. Some will hold up well, while others will not. Given the cost of a quality can, plus the cost of the transfer and stamp, I would not want to run the risk of destroying the can (or voiding the warranty). Again, the manufacturer will know.
Regarding your question on drop: 1 MOA = 1" @ 100 yds. and 10" @ 1,000 yds. So, if my math is correct - you would need 38.6 MOA of dia- up to hit your target at 1,000 yds. This means that you would need a scope with a 76.2 MOA in total travel. This is a tall order for a 1" scope, although I suspect there are a few out there. To be sure you have the capacity, you would need to mount the 1" scope on a 20 MOA rail. Or simply go with a quality 30mm tube. Read the specs on the scope you intend to use. Give yourself another 10 MOA cushion as ballistics and real life results don't always mesh. I have often found I need a few more clicks over my computer generated drop tables to actual hit the target at longer distances. Good Luck.