The engine is 1970-71 model year, and I would say it's original.

Impulse starter, G3 carby, no decompressor, and 'boxy' VC-style muffler are all correct for that model year.

The '68-'69 had a 'torpedo fishtail' style muffler and G2 carby, but I can't find a definite reference for the '69-'70.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."