Is the early rod 130mm long or 125mm. Not sure what one to buy, my calipers don't go over 100mm.  The online listings show it as a 431 rod. Someone is selling two lengths with the 24mm crank pin.

My 1968 DT1-250 has a 130mm rod with a 24mm crank pin and 18mm pistion pin.  Got my set off ebay:  EARLY Yamaha MX250 DT1 250 130mm Long Connecting Rod Kit w 24mm Crank Pin NEW! | eBay     Note:  I ordered the 125mm first and had to exchange, recommend pulling and measuring before ordering.

The Piston port 250 models use the longer rod, the reed valve motors use the short rod.

On my Canyon bike, I used a '70 (piston port) cases with the short rod & used a later reed valve cylinder.
It's worth a few h.p.