If you are adding a HPR, then there are no other parts you need with it, it comes complete (ie the tabs and seat you mention are not needed)
You might want to consider adding the new DSV instead of a standard mouthpiece, if not then you will need mouth piece mushroom valves and if the RAM does not have a mouthpiece with it, you will need to wagon wheels as well (you can reuse the originals if you have them). I would also add a set of hose clamps, yours might be OK but many are brittle and considering the cost of new ones, I see no reason to use old ones unless you are trying to keep the reg original.
Keep in mind there is no way to monitor your gas supply with a DA or RAM, something I highly recommend you do. You should use the reg with a WORKING J valve or a banjo adapter to monitor you air supply. If you choose to use a banjo, you must have a long yoke to use it. If the RAM does not have a long yoke (some do , some don't) , you might want to consider trying to add one of those too. If Bryan does not have one, Rob at the Scuba Museum might.