Start hunting for the right motor mount bracket. A 292 used a different bracket on the frame and a 250 one will not work. I agree with Jerry on the cam, it should be a good choice with single 350 or 400 cfm four barrel. Three carbs are cool, and you might get them to work, but it won't be easy. I am not sure how they rate the cfm on them, but in normal driving, you would only be running on half of each carb. They are a two barrel design using the second barrel for full throttle operation.
No need for head work other then cleaning out the casting flashing and getting a decent valve job. I don't think I would even bother with oversized exhaust valves. The intake to exhaust air flow ratio is pretty good to start with, no need to go messing with it.
If you know the history of the engine and feel confident in it, then just clean it and go. But if there is any doubt, pull it apart for a proper cleaning and inspection. You can re-ring one if the bores check OK and reuse the original pistons. If it needs bored, add propane pistons for a easy compression increase.
I have run a pretty stock 250 at the local drag strip with single exhaust then backed it up with headers, with both running through a 2 1/2" single exhaust system and both times with in the same week under the same weather conditions. All the time slips were identical, the header made no different at the stock rpm (4700 shift rpm) I was running the engine. The original exhaust would have been 2" or smaller, so my 2 1/2" wasn't the choking it at all. Stick with original 2.5" opening 292 truck manifold with a single in, dual out muffler with 2" or 2 1/4" tail pipes. You need to keep the pipe small so the heat can keep it dried out.
HEI is a excellent distributor, no modifications needed to it. 12 to 14 gauge wire, bypassing the resistor wire, straight off the key switch. You do need IGN 1 & IGN 2 tied together at the key switch so the distributor gets full voltage at start and run.
Have fun, Joe.
