</font><font color="blue" class="small">( What current GT has the capabilities of the 318 )</font>
I don't think there is anything that resembles a 'traditional' garden tractor made today by anyone that comes close to what the 318/322/332 were. Meaning beef, almost-SCUT configuration, in the 48" wheelbase (more or less) size. The Deere X-series is close in beef/features and there are a few others that might come close but far as I know they are all the larger framed (typically 4 1/2 foot wheelbase) GTs - considerably larger than the compact 318.
</font><font color="blue" class="small">( I would expect a Kaw v-twin )</font>
While they definitely have their good points, I'm not sure that any of the current typical GT wondermotors from Kaw, Honda or anyone else are quite comparible to the old Onans. Something over 750cc, and as much torque as a few low-end CUTs. Only thing I see wrong with the Onan is it is a bit thirsty.
I bought mine at a good price, but as things go the used Onan did turn out to have problems. I won't get rid of the 318 though, I believe I'll drop a new Onan into it. The rest of it is rock solid (knock on wood) and there's just nothing out there quite like it at any price, and the new tractors that even come close are 2-3 times or more what I'll have in it.
I think the only thing that might be better than a 318 would be a 332 but they're pretty rare around here.
Would I buy a 2004 version? If Deere could keep the price under $7500, re-do the optional rear PTO for 540 rpm, and include the diff from the 400's (locking) it woud be very tempting. In other words base it on the X-series but in 300-size, call it a "X365" model.