window replacement--lintels? Information, help and advice on many architecture, self build and design problems and issues

[notsohandyandy]

Hi All--"new poster" Alert.
My house is fitted with slightly worn hardwood windows which only have a 12mm d/g gap, and I'm looking to replace them with the better sound and heat insulation of (relatively) maintenance free UPVC. The windows will be going into the original Victorian brick-arched openings; when the existing hardwood windows were put in by the previous occupier, some work was done on the inside to tidy up the plasterwork, and the top and sides of the internal window reveal have been reconstructed.
My question is this: given that theres been no apparent movement of the brickwork in the 20 or so years that the existing windows have been in, can I assume that theres sufficient structural strength at the head of the openings and do a straightforward replacement without exposing the internal brickwork and checking the condition of the lintel? The openings in which I'm looking to fit replacements are on average just under a metre wide and around 1700mm high: had there been a problem with the window structure, would the existing hardwood windows have been of sufficient strength to take the weight of the brickwork above, and might the installation of UPVC expose any weaknesses? Lastly (long shot, this) is there any way of checking the adequacy of the window support without exposing the internal brickwork?
Sorry its a bit long, but any advice would be appreciated. Ta.

[notsohandyandy]

While waiting for my post to be moderated, Ive been doing a bit more searching. Unless I'm reading the links Ive been looking at incorrectly, they seem to be suggesting that in openings of this scale the arch itself forms the structural support for the brickwork above it. Wouldnt there also be a wooden lintel on the inside?
Probably fussing over nothing because I'm almost sure that when next door had their very similar windows done, it was just a case of "whip the windows out and pop the new ones in", but better a properly planned and finished job than a pile of bricks where the wall used to be--or worse.