For those of you wondering about the redesign, here's an update. I have indeed been working hard on the project and wish things could go quicker but I need to keep the day job which certainly takes up a good bit of the day.
First thing I did was to build an accurately dimensioned wood mockup which could be bolted to the gearbox studs in the correct position. This would allow me to mount 350 or 500 top ends to it and get feedback on the ideal V angle. This V angle should be the best compromise in terms of smoothness, easy fitment into the frame, allow easy removal of top ends with motor in frame and allow all this with either 350 or 500 top ends. I also got familiar with the 500 cases and top end. Some interesting things I've discovered from the 500 and progress so far:
1. Had never really been sure about this but having made measurements myself, I can say with certainty that the 500cc crankcase castings seem to be identical to the 350 except for the machining of a larger diameter cylinder mouth and slightly different stud locations. This fits in nicely with my own intention which was to design the new castings such that either 350 or 500 top ends can be fitted, depending on preference.
2. This one was the biggest surprise. Discovered that the 500 head, which looks rather massive is actually MORE compact than the 350 in the area of the intake manifold! Yes sir, the 350's intake 'protrusion' is actually longer and sticks out further than the 500. Thing is, the rear cylinder head intake in the V twin must not foul with the rear frame tube (which goes downwards, roughly under the seat and ends up at a "T" junction, bolted to the rear engine mounts. With several iterations of V angle changes, I found one which should work well in this regard.
On a side note, the 500 head seems really beautiful to me...that stack of fins which splay straight, tangentially on either side of the exhaust port, while the fins above continue on their inward curve, following the geometry of the rocker covers- pure aircooled art!
3. The next good thing which also seems well within reach is retaining the stock rear engine mounts. The first Musket engine needed modification of these mounts to allow the entire crankcase to shift slightly forward and up. As those of you who have removed your cases from the frame know, the engine is a stressed member, with the frame bolted to the front and back. The back is somewhat "interesting"...for those of you who haven't taken it all apart, here's how it goes;
a. The crankcase is bolted to the gearbox with 4 studs.
b. The front engine mounting plates are bolted to the front of the crankcase and the frame's front (down) tube.
c. The REAR mounting plates are in 2 separate pairs- an upper and a lower. The upper pair of triangular plates are bolted to the top of the gearbox and the lower pair of plates (which also serve as mounts for the center stand) bolt to both the bottom of the gearbox and the rear end of the crankase.
The new engine should be much easier to install as all the rear engine mounts can stay "in situ". Here's how it should go if your stock Bullet is standing on its center stand, eagerly awaiting its heart transplant:
a. Remove tank and clutch cable from the clutch lever at the handlebar.
b. Remove front engine mounts.
c. Cut main wiring harness somewhere halfway across 'backbone tube'- this is the frame tube under the tank.
d. Cut the backbone tube right in the middle.
e. The entire front section of the bike can be rolled away as a unit- handles, forks, wheel and all.
f. Remove clutch case components- primary chain, sprockets, inner and outer covers etc.
g. Unbolt the 4 studs connecting cases to gearbox and remove stock crankcase. Gearbox stays in frame.
h. Install v twin crankcase by bolting to gearbox with same 4 studs.
i. Install custom FRONT engine mounting plates to front of cases.
j. Install frame 'backbone tube' extension piece to where frame was cut.
k. The front section of the bike that was rolled away can now be attached to the rest of the bike through the front engine mounts and the frame extension piece.
The frame extension piece can be welded permanently which is preferable, but it is also possible for it to be attached rigidly with cross bolts.
Ofcourse, there will still be other things to take care of but the bulk of the installation should be done.