You don't want to run a MAF. The MAP is built into the MegaSquirt board. For fuel, you want the coolant temp sensor and the intake air temp sensor for sure. Getting GM sensors from just about any vehicle from like 1988+ work. Coolant temp sensors work fine as intake air temp sensor as well, particularly when running boost. You can find a point to thread the sensor into the intake charge pipe and you'll be good.
Your wideband O2 can be wired right into the MegaSquirt. Depending on model, it may support using both the gauge and hooking up to the MegaSquirt (two programmable outputs).
I don't even have a TPS on my OHC L6 right now and the only side effect so far is a slight hesitation coming off idle from a stop, otherwise it runs just fine. Though some things are harder to tune without the TPS and associated data.
You would only need a crank and cam sensor if you are going to sequential fuel injection or distributorless coil packs. You can control timing with out those by simply hooking the "tach in" wire of the megasquirt to either a points contact or to an HEI pickup coil, then the "IGN out" wire to the negative side of the ignition coil (with +12v on the positive side). You would have full ignition coil control at that point.
If you definitely want the extra extra precision of sequential or coil packs like on my OHC L6 project, you will need a trigger wheel and crank sensor, which I've bolted a universal one to the front of my engine and used a $25 hall effect sensor from digi-key, but any pickup sensor you can come up with works. Stock Ford VR crank sensors are rugged, common, cheap and popular.
The cam sensor can be made in a few ways from an old distributor. You can smooth out all the lobes except one on a points distributor so the points contact opens only once per distributor rotation and that becomes a cam sensor, or like my Buick I took an HEI distributor and ground all the pickup coil and reluctor teeth off except one each and that creates one pulse per distributor rotation and makes a good cam sensor. Or like I did on my OHC engine and cut down the distributor in a way to create a tab and got a hall sensor to read the tab as it spun by. The most difficult part of the MegaSquirt is having sooo many choices.
