I'd start it at 425F(210c) and then drop it to around 325F(160-165C) as soon as I put the roast in: starting it hot often gives better results than keeping it the same temp the entire process.
After that, you're going to want to cook it 20-30 minutes per pound (if it's a butt roast, you might bump that up to ~40 minutes). I'd start checking it with the thermometer at the very bottom end of that range, and take it out of the oven before it hits your target temperature.
I do NOT recommend 160F(71C) degrees as your internal temp, unless you like shoe leather. The USDA believes everything should be cooked to a cinder: trichinosis and salmonella and most other common nasties are killed at around 140F(60C) (144F is the instant kill number, but it's pretty hard to get your meat to 140 without it staying there for the 60 seconds that would be needed to kill everything). You should take the pork out at an internal temp between 140F and 145F degrees, to insure that the internal temp hits 150F(65C), which is a good safety margin.
Internal temperatures will continue to rise after the roast is removed from the oven. If you remove it at 160F or 165F it'll be 170-5F before it stops cooking, and that's flat inedible IMHO, and in no way pinkish. If you feel that you must wait until it hits 165F, take it out of the oven at 155F, and it will get to 165F before it peaks.
(Insert disclaimer about undercooked food blah blah blah...To be 100% safe you should cook it to 1000 degrees, then snort the ashes)