Continuing with a bit more info....it has the square section swing arm. Keen to know whether others agree that the wheel rims can be a reliable source of the bikes age. I would seem this is a Japanese DT as we didn't have a factory in Australia. It came with a brand new battery still in the box and a spare tool cylinder. Obviously I'm hoping that the spare motor and frame are first model DT1 250.

do you have pictures of the bike and engines? we love pics here and it will certainly help here. there is also some 1968 DT1 gurus here,namely Enduronut.

one giveaway is besides the ignition switch bracket located under the tank but all the 1968-70 DT1s have this.another give away is there is no turn signal brackets on the rear fender loop,that is if the numbers are correct and the frame itself is unmolested.
here is a pic of one of my 1968 DT1s,I do not have the second one assembled currently.

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Thanks Bigdog - pleased to report that the frame does have the ignition holder bracket under the tank and no turn signal brackets at the back.
I'll take some photo's soon and post them on this site.
I also had a look at the old tank, which has cracked, faded and flaking purple paint but maybe looks like it might have been the golden orange colour originally. I wonder if all the first DT1's were white, like the USA models, or if the Japanese ones that came to Australia were a different colour?? After further research I've concluded that they're all Japanese...not sure what I read to make me think there was also a Yamaha factory in the USA.

fantastic! looking forward to seeing it. there is quite a few members here that have 1968 DT1s. this bike is well represented here! the late 1968 DT1 happens to be the rarer of the 1968 DT1s.it should have 1969 to 71 tank mounting so the fuel tank is no where as expensive to get. yours was made right at the end of the 1968 model year,just before the 1969 models came out.

they made roughly 1500 to 2000 of these late 1968 models. most of the ones I see have the infamous bolt on tank under bracket.

The bikes intended for other countries, including those for the Japanese Domestic Market (JDM) often were issued in different colors or paint schemes than those in the US. Enduronut and I are in the process of building a database that hopefully will eventually contain as many of those variations as we can document. It is a huge project, so be patient with us

Here are some photos that might be of interest - my earlier post was incorrect sorry; it does have rear indicator lugs welded to the frame.

I've got a stack of photo's and very keen to hear comments on what they might mean for identifying the bike.

More photo's including some interesting bits that came with the bike - amusing to read the text on the front of the battery if it's not too small; why would they say this???

it has the 1969-70 swing arm on it too as it appears. the swing arm on a 1968 DT1 was a 1 year only part.

all the 1968,1969 and most 1970 DT1s had a square tube swing arm. the later 1970 and all 1971 DT1s had a round tube swing arm. I have seen 1970 DT1 Cs with the round tube swing arm but then they could have been swapped. one of the downfalls handling wise of the DT1 was a short wheel base and the RT1 had a longer swing arm that would bolt right on and all those were round tube.

that frame looks like a 1969-1970 frame. the 1971 did not have the key switch boss on the frame as the switch sat between the tach and speedo.

here is a 1968 DT1 swing arm.

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Nearly there....I hope these are of interest and I will add further comments on individual photos once I get them all loaded.