From the point of view of the amplifier, all it cares about are the relative impedances (electrical resistance) of the two speakers.
If they have very different impedances the amplifier could potentially end up driving more power down the lower impedance channel than the higher impedance channel - This may mean a 100W amp (for example) would be driving one speaker with 55W and the other with 45W (though it's unlikely to be that unbalanced).
As the amp is relatively old, there's probably two completely separate signal paths through the amp, with separate electrical (rather than electronic) amplification on each channel - the left channel will act exactly as if you had a matched pair of 7seMk3's, and the right channel will act exactly as if you had a matched pair of Akai 40W's. The two channels are sharing a common power source, so this is where the uneven power distribution, as above, would come in.
From the point of view of the speakers, they may get a little more or less than half the amplifier's power, but provided the amount of power if within their input tolerance, they would not suffer.
As for actually listening to anything on your system, I hope your amp has a 'balance' control. For line-up, ignore the bass - that's not used heavily for localisation of sound - aim for a centred human voice to sound centred, and you'll probably be fine. Having a tweeter on only one side might be a bit weird, but I'm sure you'll get used to it!