I'll wager the reason for most of the cut-off support tops was to facilitate removal and replacement of 216's without having to go through the misery of taking out the 43 million nuts, bolts and screws which hold the front clip on, and to prevent paint damage to all of those parts upon reassembly.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission