If it needs very thin oil then it probably has. The 1.3 has a timing chain which is one less thing to worry about I suppose. Not sure what the turbo engine has though. I wonder how easy or difficult it would be to put a 1.3 engine in a 695 body? Somebody is bound to have done it. A Toyota yaris 1.3 engine would probably be a good replacement for a knackered 695. Electrics and the gearbox would probably be the biggest stumbling blocks I would guess.
The 659 has a timing chain too. Bigger/better intercooler http://www.dsport-web.com/copen/74.html With steel intercooler pipes http://www.dsport-web.com/copen/62.html Bigger turbo kit with larger injectors http://www.hks-power.co.jp/en/search/vehicle/399 If I was going this extreme, I'd put a metal head gasket on.
Getting to the plugs is easy enough, just get the engine cover off, then remove the Blow off Valve & pipes to get to the coil packs. In the service manual it gives two numbers (both iridium types): SK20PR-A8 IFR6J Electrode Gap 0.7-0.8mm Change plugs ever 36,000miles/60,000km
I fitted a new kitchen in my house last summer and it still isn't finished. That engine change would be more like a 6 month project. Not including the alarm though, that's another 6.
Found this on a NGK site http://ngk-sparkplugs.com/bkr6es11-p-1959.html cross refrences BKR6ES to Denso IK20 and VK20. Only £1.50 each on ebay. Will give them a go.