Ok to clarify a few things....First only 65 and up 427's had screw in freeze plugs stock from the factory. Second there is no such thing as a 390 sideoiler from Ford. There was however a sideoiler kit (made by FPP possibly?) that did allow a std FE block to become a sideoiler using external tubes running to the center three mains through hollowed crossbolts. Pretty cool! anyway back on track....sorry about the head numbers. They are ON the heads between the center two spark plugs. Not underneath on the block. I should have been more clear on that. The 9C11 you found on the block is the date code of 69/March/11. It's also very possible there is no casting number on the block. There was a batch from 68 with none and I think another from 69. Being you covered most of the block very possible. I'd check the stroke through a spark plug hole. Rotate the engine to TDC and put a wood stick or dowel or stiff wire inside till it rests onto the piston. Mark the stick noting a common edge to use. Then rotate to BDC and mark again. Remove stick and measure between the lines. This will be the stroke. A 3.50" stroke is a 352 or 360 crank. 3.78 or 3 3/4" (to make things simple) is a 390/427 stroke crank. And a 3.98 or 4" a 428 crank. The 5TE exaust main's are from a truck. The "TE" part of the number denotes a truck application. The two bolt holes you see on the block are where the "J" bar was attached at the factory to move the block along the assembly line.