Info provided by Eric of UglyBoost91 Youtube Channel
From the factory, the Vortec 4200 was only ever available with the GM 4L60/65E automatic transmission.
The problem on the Atlas series engines is; Not only is the bellhousing bolt pattern, starter position, and flex plate/flywheel ring gear O.D. unique to all Atlas series engines (4,5 and 6 cylinders), but the Vortec 4200 6 cylinder itself has a unique crankshaft bolt pattern not shared with it's 4 or 5 cylinder siblings, or any other GM engine!
Thankfully, GM had intended to offer the 4200 with a manual transmission in overseas markets, so the basic hardware is mostly there. Below and on the Sub-pages, you will find information on Vortec 4200 manual transmission specifics in general, and also those specific to a particular transmission adaptation.
General Vortec 4200 Manual Transmission Facts & Information:
As discussed previously, the Vortec 4200 has some "unique" features and dimensions:
Bellhousing Bolt Pattern
The Atlas 4/5/6 engine family has a unique bellhousing bolt pattern. It is not shared with any other engines, and despite rumors that the GM FWD / "Metric 60 Degree" pattern is close, it's not by a mile. Thankfully, GM located the Dowel Pins and their corresponding bolt holes in the same position as their V8s, including LS, SBC, BBC, B-O-P-C, etc. Because of this, adapters are available for purchase, or you can make your own. More specifics are available on this topic here: Bellhousing Adapters. However, not every manual transmission needs an adapter, including the AR5, AX-15, etc...
Ring Gear Size
The Atlas 4/5/6 engine family has a unique bellhousing ring gear size of 161 teeth.
Starter Position
The Atlas 4/5/6 engine family has a unique starter position, which is high on the left side of the engine. While great for preventing water getting into the starter, on swaps with GM V8 transmissions, this will require modification to the V8 bellhousing.
Crankshaft Bolt Pattern
For some reason, the Vortec 4200 is ultra unique in this area. It shares a crankshaft bolt pattern with NO other engines, not even it's 4 and 5 cylinder Atlas engine siblings! The crankshaft features 8 bolt holes, M10 x 1.00 (Same as the Ford Modular family). The one commonality it does have with other engines is the pilot bore. Both the flywheel pilot bore and the pilot bearing O.D. are the same as the LS family, and LS pilot bearings can (and are) used in some swap applications.
PLEASE NOTE: 2002 and some 2003 engines came with a M10 x 1.5 flywheel bolts. There is currently no Flywheel rated Fasteners available for this thread in the right length needed.