Inliners International Forums General Discussion Engines Is it a 261? Number on block is.....

Tecnically, the casting number for the head is on the drivers side near the valve cover.
The numbers you have are the date code, "B51" would be Feb. 5, 1961.

I believe it is an 848 from a 235, as all the ones I have seen have the 848 850 on the pass. side and "848" as part of the casting number on the drivers side...