Aluminum heads? Roller cam? Stock oiling system? etc? FSM will be sort of a guide but you'll probably want to ask lots of questions on here.
First thing you will want to do is very carefully disassemble it and I would check all clearances, end plays etc. I would even write down every fastener torque value as you go and take a ton of photos. Don't throw away any old parts either, you may want to go back to them for reference before ordering new ones.
Indy Cylinder Head 426-1 CNC 285 heads. Solid roller lifters, although I found a plunger for a hydraulic lifter in the oil pan today. Cam has a bad lobe on it. F1 Procharger at 10 PSI of boost.
Disassembled the engine today. Got some info from the rotating assembly. Eagle 7.1" H beam rods. Crank has these numbers on it, 4.500x2.200 BBC, 839, 59. Could it be a 4.5" stroke? No numbers on the pistons, but the top of the wrist pin is in to the oil ring.
#2 piston had a portion of the ring land broken. That cylinder wall is pretty scratched up. The rest of the pistons had some light up and down scratches in them, and some had a lot of detonation, like little weld spatter craters.
Rod bearings looked good, crank bearings not so much. they have light scratches in them.
The engine goes to the machine shop on Friday. See what they think of it.
Tried to measure a piston diameter. I come up with 4.26". Measured the top of a bore at 4.28". When it was still assembled there was a lot of distance between the piston and cylinder wall. I could not measure it, but I could see the top ring sitting in there.
I am trying to measure the stroke of the crank. I am thinking to put the crank and a piston back in, put the piston at bdc and meaure the distance to the deck, then put the piston at tdc and measure to the deck, (the domes rise above the deck). Add the numbers and that should the stroke. Will it work?
Tomorrow I plan to clean up the heads and see if there is anything going on with them.