660 in another frame

will I be able split apart af new smc 660, and put it into a 620` 1994 frame?

Ulves

No, you won´t! The engine case is longer than in former times because of the balancer shaft, which was added to the engine from 95/96 on and which needed its own place in front of the crank case. So the frame of 94 is too short for an engine with a balancer shaft...

Idna

there is no balancer shaft in the smc660, thats only for the 640` as far as i know.

As far as i know, all engines from 99 on are equipped with the balancer shaft, even the "sports-"engines of SMC and SXC. But it makes no difference wether the balancer shaft is placed or not, because all engines from 96 on have the case for the balancer shaft. So you are definitely damned to fail with your attempt...

Idna