Does anyone know the dimensions for a 1971 RT1 Woodruff Key?  Thank you!

Buy a correct yamaha key.

What Capn said. Done.

or just carve one out of a thick washer with the right curve. On my lawn mower--alloy key--i cut one from the corner of a yamaha head steady or front engine mount from an IT250 i think it was. Mind you i'm running out of corners as broken it 3 times hitting a tree root. Saves the crank getting twisted though, Chinese ohv motor with a heavy steel flywheel. If ya taper is good you could make an alloy one if easier because "in theory" the key is only to locate the flywheel. But of course often people don't do them up near tight enough &--broken key again. On my TT250 i experimented with advancing the flywheel so had No Key & never caused a problem but crank & flywheel taper were perfect. Mind you i 'do' overtighten things. Do it up till it strips then back it of a bit lol.

Thanks for everyone's help!

Thanks, Dave and Pedal.  Probably good advice, just looking to save some time.

I guess ya not in the UK but just saw this by googling.
yambits.co.uk/rt1-flywheel-woodruff-key-p-30256.html

Hey RT, I had an old key that was close and started grinding on it but thought it might be futile.  Yea, good point about not REALLY needing it except for alignment.  As far as tightening, would you go 10% over spec on the torque??

No sir, USA.

I am not a Yamaha expert but the fit of the woodruff key is perfectly line to line with crank and flywheel and made from some pretty nice steel. Costs way more to manufacture than a washer stamped from 10xx carbon steel, I assume the engineers did this to remove any play that would otherwise damage crank and flywheel. Personally I would get proper key and torque to spec.