Assuming the bike fits you well, easy.

1. Stem: use the one you have, if looking for a more upright position; add 1 or 2 cms. if trying to approximate present fit.
2. Bars: use "mtb" flats, with a bit of back sweep, plus bar ends if trying to approximate present fit. Try other variations, as some mention above, if looking for something different.
3. Shifters: you may have to check. You should still be able to buy the last-generation 770 10 speed shifters. They'll work; the new/current Tiagra 10 spd. ones probably will as well, but you should check that (cable pull).
4. Brake levers: you need flat-bar (mtb-style) levers, but for road caliper/canti brakes, not v-brakes. You can, if necessary, use Avid SD7 levers; they will adjust to work with calipers.

All this can be assembled quite inexpensively. As giantfcr1 points out, costs much more to go the other way.