Honda-SOHC

OK, I was going to start a new topic but decided to keep it in this thread.....one of the final tasks on this bike is to refurbish the wheel rims and hubs as they're somewhat grotty! 
I've removed the rear wheel and de-spoked same in the hope of resurrecting the rim but it's pretty badly pitted and there's lots of rust on the inside.  I tried cleaning it up but it still looks crap!
I did some initial research into replacement rims and while doing so, checked the tyre that I took off the rim....it's a 4.00-18 Dunlop K81 TT100.  The tyre itself is in very good condition but is not standard size for a 500. I then checked the front tyre and it's a K81 TT100 but 100/90-19!  According to the general specs for a 500K1 the tyres should be 3.25 and 3.5 respectively F and R.

Back to the rim search and I've found that Motorcycle Yamiya sell a D.I.D rim kit (F and R) for the 750s at a competitive price, even when adding on the exorbitant freight costs.  I'd rather buy from them than cheaper rims from Thailand.  If someone knows where I can get D.I.D rims or equivalent at less than $330 (AUD) shipped to my door then please let me know!!  (Re-chroming the current rims would cost me more than this!).
Finally, should there be any dramas in fitting the tyres that I have on 750 rims (assuming that the current rims are std 500 jobs)? 
TIA

Thanks Roy,

I see you have a GS1000 as a project bike...should be superb when it's finished! 

Keep searching Roy, you never know what might pop up!

I despaired of finding a CB750K that wasn't totalled, or vastly overpriced....not many for sale in AUS anyway.
So I've happened across a very nice & original '78 Suzuki GS750E  (the "C" suffix in subject line denotes model year).
Apart from a couple of paint chips on the tank, and a small dent, this bike presents very well indeed!
I've already taken it for a test ride and everything seems as it should.

Thanks Andy,
We had 3 degrees yesterday and 3 degrees today so that’s the same as your 33 (never was good at maths)
Please say hello to my Auntie Podes,

Ian, 59 degrees North, 3 degrees West, so nearly North of Everywhere.

If that's 3° Celcius then that's flamin' cold mate!  If it's 3° Fahrenheit then it's -16° C and that's (insert expletive here) cold!!!

According to the Honda Shop Manual, those figures are correct.

Honda specified Auto fluid or 20w50 long before fork specific oils came along. With the great number of dirt bikes around in Aus i would have thought that the bike shops would sell fork oil

Yes of course Brian, fork oil is readily available in all my local bike shops.   My point towards DR was that in general, EU brand names for oil are not represented in Australia (I guess I didn't make that clear earlier).  DR has indicated that he notices a slight clunk as well, which was helpful in my understanding of what goes on.

Thanks Brian and Graham, I'll change out the oil and report back.