never tried the eighth inch cranks or the tessas. But on ur seatpost diameter, take it to the shop. They'll have those seatpost sizing rods that is kinda like what people use to determine ring sizes.

Sheldon Brown also have a page of seatpost sizes according the the brand/model/year. If u're lucky u can find yours here:
http://www.sheldonbrown.com/seatpost-sizes.html
But I'ld just take it to a bike shop to get it measured.