I think you will find that oversized pistons and rings are no longer available either via UK dealers or Japan.
I found that replacing rings with just standard new ones and giving the bores a hone to bust the glaze normally sorted the smoking.
I would be chasing the guy you bought it from if I was you, your not going to get much change from £500 - £600 to do this work, If you can find some one that will do it.
Most UK dealers will have never seen or heard of a Beat, just a few that have looked after some cars if they were local. They can order parts and get part numbers using the VIN number, But prob wont have any workshop Manual information.
Most Beat parts now will have to come from Japan if ordered at a UK dealer (Alot used to be in stock in belguim, but not now) so dont be surprised if there is a long wait for them.
Steve M
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Its all gone Norfolk!!!
Now in the Lotus position.