I was looking at earlier pictures and noticed the tube welded to top bar and with a flange at the other end to accept two of the engine head bolts for extra mounts and rigidity I suppose.
I made a mod to the frame on my bike that in sort does a similar effect for rigidity, where I put two pieces of sheet metal welded on the side edges of the top and lower tubes just forward of the engine and welded them in place.
I have seen some motor cycles that actually use the engine as part of the frame and this in some way adds to the frame and cuts down on weight.
For you build, installation and removal of the engine, I could not see that close up, are the bolts that go to the top hold in a slot or do you take the head completely off?
I suppose in any case removal and torque down of the bolts mean using a star pattern so not much difference in time spent. If you loosen enough to have slack, you could just remove the two bolts, if you know what I mean?
Most importantly wanted to congratulate you on the work and wondered how you got it jigged up so that it is all in line for welding! It looks perfect.
The other thing I saw but not on any other bikes so far is the fork strengthening parts welded in place like the triangle braces on train trestles. There are no shocks as part of the fork, but the work is all homemade!
MT
http://motorbicycling.com/showthread.php?t=29678&page=7