Features of the Chevy 3899621 (621) Bellhousing

The "621" Chevy Bellhousing is a 168 tooth aluminum bell with 4-5/8" center hole.
It was used on most Chevrolet Big Blocks,Small Blocks and Six cylinder engines requiring an 11" factory (Heavy Duty) clutch.

Considering the wide range of original usage, and the fact that it was in the General Motors parts catalogs until at least til July of 1987, you would think these units would be plentiful. Yet, this Clutch housing is so highly sought after, that there is now a reproduction available.

Front View

In the view above you can see the starter bump that is common with 168 tooth bells.
See Chevy Bellhousings

Part # and Engineering Codes

Two of the examples that I own have very light casting #s, which are upside down as compared to other Chevrolet clutch covers.
Tip: Not all factory part numbers were this light of a casting, but all aftermarket numbers that I've spotted have wide numbers and no date & engineering codes.

Side View

This picture above shows the part number location, and the starter bump that is needed to accommodate 168 tooth flywheel.

Fork Side

This view is of the clutch fork side and also shows the z-bar mounting boss.

Inside View

This is a picture of the inside and shows the single clutch fork stud boss, which makes this a left hand drive only bellhousing.

Applications

0.683 Housing Assy., clutch(cast 3899621)

Thru 1975 Chevrolet parts catalog *
65       all (409) {exc. A.T.}
   69     all (427) {exc. reg.fuel}
   66-68 all (427) {exc. A.T.}
   70-74 all (454)
   72       all (402)
   65-68 Pass.(396) (exc. A.T.)
   66-69 Chevy,Chevelle,Camaro (396) (exc. reg.fuel)
   69 Pass (396) (exc.reg. fuel)
   70       all (396)
   70-71 all (400)
   67-70 all (350) (exc. Sp H/per.)
   70       all Sp. H/per. (350)
   71-75 all (350)
   66-68 all w / H.D. clutch(327)
   69 Police (327)
   68 all w / H.D.clutch(307)
   66-67 all w / H.D, clutch(283)
   65-68 Pass. w / H.D. clutch(230,250)
   65-68 Pass (taxi) (230,250) (exc,A.T.)
   69       Police (250)
   70-72 Taxi,Police (6 cyl.)

   F= Camaro
   X= Nova
   Y= Corvette

* This catalog can be confusing. All = all cars with that engine available and all vehicles covered by this catalog.
This catalog has very few pre 1965 listings, and No corvette,truck,Yenko,COPO or anything after 1975.

1976-81 Chevrolet parts catalog
76-77 all (350) W/M.T.
76-81 F (305) W/M.T.
77-79 X (305) W/M.T.
78 F,X (350) W/M.T.
79-81 F (350L) W/M.T.

1953-1981(Nov 1981) Corvette parts catalog
68-81 Y (350,427,454)

Applications per 1976-81 Oldsmobile Parts Catalog Effective July 1987
77-79 X(305) W/M.T.

Applications per the 1973-78 Truck Parts Catalog, Effective February,1985
73 G3 (exc.A.T.)(250)
73 G1,2, W/H.D. Clutch(250)
73 G-2,3(307)
73 G-2,3(350)

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 and 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!