We just got done reassembling a vn750 engine, so I'll try and help. Start with the front cylinder and finish assembly before starting rear cylinder.
Turn the crank counter-clockwise(ccw) untill the paint mark lines up with the raised boss on the case. That is TDC on front cylinder. Now ,on the cam chain there should be a paint mark but if there isn't you can chose any pin and put on a mark(we used nail polish) count up the left side of the chain 38 pins and put another mark. If there is no mark on the upper chain pick a pin and mark it and count left to right 24 pins put another mark.
Put the middle cam gear in the chain with one of the marks lined with the circle mark. Drop the chain down into the lower end and around the cam gear so the marks line up. Put the pin in the middle gear, now put tension on the right side of the chain and check to make sure circle mark is at 12'oclock.
Put in the chain guides.
Put the head on
Put the upper chain guides in secure them. Put the intake(long) cam in the head. Line up the circle mark on the cam with the edge of the head, now put the exhaust cam in and line up the circle with the edge of the head. Insert some thing into the acct hole and put tension on chain. With a straight edge check that the circle marks are still lined up with the head. If they do you can tighten the cam cap. That it for the front.
For the rear cylinder rotate the crank from the left side 305 degrees clockwise(cw)TDC on rear. On the right side there is a mark on the cam gear and a raised boss on the case, line them up. On the lower rear chain make a mark and count 38 pins put another mark on the upper chain count the 24 pins. The rest is the same as the front.
I hope this helps