Originally Posted by dracothered
In what areas do you think it need more beefing up?
That's a lot of engine to hang off that single downtube...I'd be worried about fatigue cracking at the steering tube and/or the bottom bracket. Even with thicker than normal tubing, I'd seriously consider bracing it better with some triangulation or heavy gusseting. It looks to me like it will act as a sort of spring and you're putting a lot of faith in one tube.
Just my opinion from 30 years of welding and fabrication.
You should be able to figure something to keep the look you like without compromising strength. Maybe a flat strip welded the length of the tube to add vertical load strength?
You have the skills, think about it.
If more is better, then too much is just enough.
If you can't afford it, build it yourself.