400-800m

I was reading about the 800m training, were lots of good tips came up.
The thing is myself have some thoughts about moving up from the 400 to 800m.
But there are two things I fere for.
I don`t wanne lose my speed and I´m happy with my building (185cm/80kg), is it still possible to get well in 800 and stay at 80kg. I read about the famous runner Alberto Juantorena and saw his weight was 80kg and he was pretty good? :mrt:

Just as DMA suggested, you can increase the tempo work as well as slowly extend out the special endurance work.

How tall is Juantorena. He looks to be a pretty imposing man.

I think you need to do a little more endurance work, but still need the speed reserves.