So why would someone use a Chevrolet distributor on a Flathead? Just because they’re easier to adjust? Is there a reason why they are used over a Ford stock distributor?
As the question is a bit open-ended, the answer needs to be a bit clearer.
1) 1932-1948 - Front Mounted: There is nothing wrong with the front-mounted flathead distributors (32 - 48) - as long as they are correctly setup, have quality parts in them, etc.. The biggest issue for many folks is they are not easy to work on (in the car) - and are a bit of a mystery to "modern" folks.
Their vacuum "load brake" system works fine with updated intake manifolds with multiple carbs. It is not a bad idea to update the internals (points cam and advance mechanism) to the later units (advance mechanism is key) - as the advance curve is better for a higher-performance flathead. Folks like Third-Gen can rebuild these early front-drive distributors.
A lot of guys will run a "Crab Style" version of the front-mount distributor - due to it being much easier to use more modern style spark-plug wires, is smaller, etc.. Many of the early "racing" ignitions were made from updated versions of the crab-style distributor. The most well-known and prevalent is the "
Harmon-Collins Dual Coil" distributor.
2) 1949-1953 - Side Mounted: Ford changed the front of the flathead in 1949 to use a different set of water pumps, different timing cover, side-mounted distributor, etc.. The distributor is known as the "Load-o-Matic" - and its advance mechanism is vacuum driven off a port in the carburetor. There is no mechanical advance (like earlier models). This all works just fine in a stock engine, but the minute you start "upgrading" your engine with multiple carbs, different cam, etc. - then the load-o-matic can become the "Crap-o-Matic". The advance curve is nowhere near correct, and you can't "fix" it. It was designed for a stock vacuum signal coming from a single stock carb - when you changed all that out, it no longer has the correct vacuum signal and the whole advance curve is fubared.
Will your engine run with a stock Load-o-Matic in your modified big-inch, multi-carbed, cool-cammed, finned-headed 49-53 flathead? - "Yes".
But will it have a correct spark advance curve . . . nope. There is no easy "fix" for the stock distributor, so guys have been converting Chevy distributors, running aftermarket distributors (flat-top Mallory's and such) and magnetos for years.
Personally, I would never run a Load-o-Matic on a modified 49-53 engine.
There yah have it!
B&S