hkmp5 Mike, We need a l/s picture of the block. It is easy to make a FE motor look like a SO block. The only thing you can't hide is the oiling different.
Here's what I know,
1 You can buy and convert a FE block over to cross bolt caps and make it look like a side oiler from the out side as long as you don't look at the L/S of the block.
2 Screw in freeze out plugs, You can buy theses on the FE forum. They look they close to the original ones but understand the size or threads are different
3 You need to have this block sonic checked and bore measured. The safe max overbore without doing some block filling is .030". If the block is .030" you have options. Have a custom set of pistons made for .035" over. Not cheap but will save the block for another rebuild. Here the bores over size numbers I am know. stock size, .005", .010", .015" .030", .045", 060" This would give you 6 rebuilds from stock, a life time unless you windowed the block and then still could be reused.
4 Are the caps the orginial ones to this block?? I have gone to swap meets and brought a set myself for a FE motor. I got burned on my first FE motor with thinking and the guy saying it's a 428 motor. I trusted him. I ended up with a 390 block and 428 crank. The motor was a 68 build. From now on I measure all parts before buying. The spacers look new for the side bolts. I know one of the guys on the forum sell side bolt spacers and bolts that are orginial looks. There is a trick to use black pipe and cut to fit. Have to flat spot the block for this to work. All you need is to mill inside the motor at the main supports. This makes a 1,500.00 standard bore block now worth 5,000.00.
I am going with the 428 PI block or a service block until you can get a picture of the l/s inner and outter if possible. This is also a good block. Some where a higher nickle than the standard 428. Race blocks for the 428 Mustangs. If the block is sound, it will work anyway. Just know the limits on it. Save numbers are 450-475 HP and 500-525 pounds of torque. Using a stroker kit will get these numbers easy and not over abuse the block for years. Good oiling pressures of 65-80 for street and higher for track racing. Barry R will sell you a nice 482 stroker parts that will drop in if the crank caps and block are true and don't need alignment. You just need to tell him the CC of the heads you are using and the total camshaft lift on the valves. You don't want Mr. Valve whacking Mr. Piston.:eek That's bad.
Good luck, send the pictures. Rick L.