57 Chevy Bellhousing
1957 Chevy Passenger Car Bellhousing Components
3704923
0.679 UNDERPAN, Flywheel
55-57 Pass. (8 cyl.)(exc. A.T.)
3734908
0.679 EXTENSION, Clutch Housing
57 ALL, Corvette (8 cyl.) (exc. A.T.)
This is a picture of a new old stock part.

0.679 BOLT, w/washer, underpan and extension
3755343 (cast 3733365)
0.683 HOUSING, Clutch and Flywheel
55-57 Pass. (8 cyl.)
3742027
0.683 HOUSING, Clutch and Flywheel
57 Pass. w/265
3742029
0.683 HOUSING, Clutch and Flywheel
57 Pass., Corvette, w/4BC or dual 4BC (exc. A.T.)
3729000 (13/16-16 Stud w/21/32" ball)
0.796 STUD, Clutch Fork
56-57 Pass. (w/4BC or dual 4BC)
3836314 (7/16-20 thd. w/11/16" ball)
0.796 STUD, Clutch Fork
55 Pass.
57 Pass (exc. 4BC, dual 4BC)
3738282 (5 1/8 x 2 13/16 x 2 1/4)
0.797 BOOT, Clutch Fork
57 Pass (6 cyl.)
3738285
0.797 BOOT, Clutch Fork (2 1/4" at clutch hsg. face w/4 clips)
57 Pass. 8 cyl.

Housing to Block Bolts
(5) 3/8"-16 x 1 1/4" Bolts
(2) 3/8"-16 x 2 1 1/4" Bolts
Disclaimer:
Factory correct applications are your responsibility. GM made part and part # changes with no rhyme but a reason (no production interruptions at any cost).
Application charts are for replacement parts that were available at the time of parts book printing.
My observations come from the parts I have in my collection or other reliable sources your parts may differ.
If Factory correctness is your goal, do more research, join car clubs,
forums and buy an assembly manual if one is available for your Project Car (you wont be sorry).
This is a fun and interesting part of the hobby!