Since some of this data is hard to find , there must be a few baskets near the same year, form other models that fit our bikes.
I see posts about clutches sticking, the need to keep clutch pulled even storing overnight, and know there must be a few guys out there that had used clutch parts off different bikes, as my 1978 IT250 clutch needs work, same issue, sticks, and expect to find 'fingers' worn, and from what I recall you get 1 shot at a light file on those fingers before the gap is too much and they chatter and wear quickly or break and cause damage.
So if a 79 YZ250 basket fits my bike, even though different part numbers, that information would be handy to those of us who ride these vintage bikes, vintage riders like vintage  
Will a 1K4 fit a 2K7 in these 161500 series parts for example?  I know I have the 2K7 right, closed all the many tabs I had open trying to find a basket without wear, and forgot if 1K4 was correct, but it is stuck in this mind so best guess this late.
Thanks and hopefully we can create some list of clutch parts and not have to leave our clutches pulled ever again.

Part number I see is 1W4-16150-00 and fits many other models.  Several on ebay.  

When the discs get old, sometimes they stick if bike has been sitting a long time.  Basket grooves are not the culprit.  Riding it a while will fix it OR the discs will fail and slip. 

Parts are not that hard to find usually, even a new basket in Germany on ebay, not cheap though. 

Well, your bike is 1W4. I saw an instance of 78 YZ400 w/1W4 basket and here is one, at least posted, as a 79 YZ250 and it
is 1W4.  Link is for part ref only.  Appears worn out. BTW, looks like it may use same friction plate as DT360.  Extra plate here, ball there, might fit. 

Link that ~may help from Barnett's, cross reference to at least a lot of plates. 

Barnetts Clutch Info PDF

1979 Yamaha YZ250 Clutch Basket