I realise this is an old thread, but I also am the proud owner of a 1989 Peugeot 753 Pro, 62cm frame with full Shimano 600 'tricolor' STI groupset. I bought it in 1989, second-hand, from a geezer in Watford who'd bought it new, ridden it twice and after a couple of months' ownership, decided cycling wasn't for him. I've made a few, fairly minor, component changes over the intervening 35 years, but the bike is still very largely original and still rides really well.
I can confirm that the seat tube is by Stronglight - mine's the same. I swapped the original Atax quill stem for a longer Cinelli XA one (ditto the original bars are now swapped to Cinellis), replaced the quill pedals + straps with Look (first original Delta, more recently Keos) and the saddle with a black San Marco Rolls. More recently I've had to replace the freehub (originally Ultraglide) with a more recent Hyperglide one, to facilitate a change of gearing, as UG stuff seems no longer available. That required a bit of 'surgery'... Original Shimano 600 52/42 rings I replaced with TA 53/39s at some point.
One thing I'm not sure of with yours is whether the wheels are actually original. Mine came with (and still have) really rather nice Mavic Mach 2 CD2 sprint rims, now kitted out with Vittoria Rally 21mm tubs (originally it came with Wolber tubs). The catalogues of the time showed that these sprints + tubs were standard fitment, but I'm not aware there was ever a clincher option (such as yours has) at the time.
More recently, I decided to strip back the lower part of the paint on the front forks (which had become quite chipped) to reveal the lovely chrome underneath. I'm really not sure why they decided to paint over the chrome for the '89 model year; maybe they decided chrome was looking 'old hat' by then, but I really rather like the look of the 'half-chromed' forks on mine now!