Have a copy of page 3 of Chrysler Canada's 1966 Shop Manual. The page lists the model numbers and engine displacements available in the top section. The lower 2/3's has a break down of the serial number.
First, for the serial number, the fifth digit was for the engine displacement which the Canadian manual showed two listings. The first was for SPN 200001 to 200647 : For 294648 and up The SPN started at 200001 at Windsor only for 1966.
A - 170 cid slant six A - 170 cid slant six
B - 225 cid slant six B - 225 cid slant six
C - 273 cid V8
D - 318 cid V8 D - 273 cid V8
E - 361cid V8 E - 318 cid V8
F - 383 cid V8 F - 361 cid V8
G - 413 cid V8 G - 383 cid V8
H - 426 cid V8 H - 426 cid V8
J - 440 cid V8 J - 440 cid V8
The top 1/3 id the sheet lists the 440 V8 was optional on models BP2, BD2, BC1, BC2 and standard on BC3 and BY1. The 383 was optional on BP2, BD2 and standard on BC1 and BC2. Nothing is listed for the 413 and 426 engines.
Looks like Chrysler may have had problems getting the 440 into production. Thus the first 4,647 cars did not list the 440 on the engine list. After that the 440 was available.