What about the auxiliary air intake manifold on
the rear of the block. If that is there its probably
a high speed. Standard carburetors are marked
also so not having a visible mark doesn’t mean
its not a high speed. With out the auxiliary air
intake it would be a standard with high speed
cylinders at least.
There is also a serial number stamped into the
block, under the cylinder, on the starboard (right)
side. Does it match the number on the tank?