[MAStuart]

I have a small block. I have been using it as a mach up block in my coupe build. A friend got this from a friend with an inside from ford. I was told it was a pre production boss block. I have to say no its older than the new boss block. Kind of a shame it sat in his shop and got rusty and has been sitting in my shop getting more rusty. The block was new and is standard bore. Well it needs to be honed to standard bore. Cam bearings are installed, has thick main caps, that are marked S V O on the three center main caps and has main studs and nuts marked ARP. There is a large R and two sets of XXX' in the lifter valley. The rear main is marked YR3M and also B50 There is other casting numbers that I cant make out. Weight of the block is 142 pounds with the motor mounts on it. Can anyone tell me exactly what this block is.
Mark