I don't know if the OP is still on board here, but changing to 700c will change the pad-dive angle considerably, and problematically so if the rims are on the narrow side.

What this means is that the pads will be occupying a vertically wider swath of the rim's side wall (or braking track). This is more of a problem with 1) rims having a narrow brake track and 2) rims that are much narrower than the tire (making the pad's more-vertical travel path possibly cut into the tire sidewall as the pads retract).

I've found even the Trek touring bikes to have very little clearance for fenders or even a tall tire, so 700c gives 4mm of additional vertical clearance vs. 27" assuming the tire cross-section is kept the same.

I've put quality Araya and UKAI steel rims on bikes that came with alloy rims, not a problem if it is for dry-season riding and using correct brake pads.
The OP needs alloy rims though.