do you already have the .357 handi' in your possession? if so, some of the .357 mag' dies are adjustable/workable for the .357 maxi'. my hornady custom grade, new dimension (series ii) titanium nitride dies from
www.MidwayUSA.com are labeled for use with .38 spec' through .357 maxi'.
by the way, the same series die in .44 spec'/.44 mag' is not labeled for the .445supermag', but looks like it would handle the extra length of the brass.
the reamer should be capable of giving you a proper chambering if it has a good pilot on it and if it is handled carefully, following the instructions to the letter. a good oil/lubricant and a careful, slow approach would let you get it all done at home with the barrel held in the vertical/straight-up position. (remember, however, reaming done by hand would usually(?) involve turning the reamer in one direction only, just like a machine does. it is possible, of all things, to ruin some reamers by turning them in the reverse direction while working with ordnance-grade metal to back 'em out!)
if you are mechanically inclined/adept at using tools then you should be ok with the chambering if you take your time and study the operation beforehand.
take care,
ss'