I'm guessing you bought the 20mil DM that was on ebay right? cylinders need fixed and I can't remember the condition of the crank... I'm running an 18mil cheetah triple in a Lonestar hill chassis.
I would run Mattoons 10plate clutch set up with Mattoon billet cover ( the billet cover is a must if you're going to kick start it and not use a roto start) and probly 2:68 straight cuts
Mattoon cases, make sure to have the shift fork window put in
Mattoon bearing support
There is a lot of debate on what trans to run, every builder has their own opinion and so do a lot of personal owners, I'm running a Robinson now but want to try a billet 2nd 2-5 and see if it will hold.
You're going to be in the 200+ hp range, so there is not a "right or wrong answer" this is one of those problems you will have to be prepared to deal with.
As for the ignition, a lot of people have started running the MSD setup... I'm running a Twister modded triple ignition (snomo) currently but a switch to the MSD might happen someday.
I would let a builder assemble the motor, so you know it's right the first time... a triple can be very costly if not setup correctly. Just don't try to cut corners on these motors or you'll fight it everytime.
Pipes will need to be made, putting it in a hill chassis make sure the pipes will clear the frame.
You'll need to run 2 pumps for the carbs most likely as well, 39-45mm to carb of your choice.
You're gonna battle chassis setup too... but that's a whole other issue, lol