As I recall, the 52-54 passenger cars had the side mounts. The 51 still used the front plate to crossmember. Some previous owner may have replaced the original 216 in weltertm's 51 with a 235 (or replaced the Powerglide with a manual?) I do not recall ever seeing an original 235 with a manual prior to 1953. It is somewhat of a moot point, as wetertm has what he has.
Here is a
link to the Chevrolet master parts catalog showing the various front and side mounts. As I recall from my 1951 Chevy, it used two separate front mounts, not the single center assembly. I just looked at the front plates on a 1960 261 and on a 1954 261. The plate on the 54 261 has the holes (and a "doubler" plate) for outboard mounts, but the 1960 plate does not. It is not obviously apparent that the 1960 plate has enough metal to accept the 1951 passenger car mounts. You may need to adapt to the center forward mount, as suggested by JiMerit. I installed a 1954 261 in my 1951 back in 1959, but I have never directly participated in swapping in a 55-62 block. You might want to try the
Inliners' site, as they are more into cars.
Hoyt
