Does the code have to do baro updates *while driving*? Just have it do the baro lookup on ECM-on, engine-off on startup, that seems to be effective enough for a LOT of other control computers-Megasquirt and Motec included.
I had initially planned on a full-pneumatic method for the boost bypass valve, that's what I use on the datto. It is "OK", but not great for street driving. It results in a non-intuitive engine response, which is...interesting. Roll on the throttle a normal amount and it makes 120-130kpa from 1500 to 3000RPM, but then once you're rolling a steady 3000RPM it vents the boost with a Whoosh-hiss, and you're driving on the very loud bypass. This gets irritating at highway cruise. (it's loud because the intake mods I did effectively remove all the sound baffling from the supercharger.) Toe in it slightly, it kicks the bypass valve closed and you're on boost, 155kpa at the current drive ratio. The blower is ported to be turned a LOT faster-target is 200kpa while keeping IAT's under 120F. It's balanced at a bad spot, as under cruise conditions the pneumatics tend to throw boost at you while holding a constant throttle position as the loading of the engine changes due to hills or even headwind/tailwind. I'll add an output the the MS2-Extra controlling that car at some point to drive the valve.
I am now considering using one of the EGR solenoid outputs, as it isn't looking like EGR is going to be a priority to keep-I wanted to keep it for the highway mileage advantage but it's easy enough to dispense with and just run a slightly different cam profile to obtain low-throttle EGR. IIRC the L67 uses a simple on-off method of boost control, so the EGR solenoid should have no problem with the L67-style boost control valve. This is the "preferred" method, as I can "lock out" the supercharger under highway cruise.
As far as the belt drive, that I won't be able to make progress on until I get the block back from the machine shop and get the heads dummied up with the complete camaro accessory drive in place. It is looking like I will have plenty of room to add a pair of idlers on a "pulley bridge" similar the the supercharged 4.6L ford engines. I'll have to do some finangling with the water neck, but since I am going to run the mechanical fan I was gonna have to do that anyway.
For the fabrication...I use a 4.5" angle grinder for a LOT of the fine detail work, it's amazing how good of a job can be done with one. I am likely gonna skin the top of the 3500 intake today, and look at what it will take to cram an intercooler down inside it.