long barrel is an MCA, carbine is an MC. The difference is the comb height. 1924 had a straight down bolt handle, swept back was introduced in the 1950s for scope clearance. Not an expert, but do own 2.
Mike

Rich
Look on the left side of the action, you will see the proof marks also a 2 digit date code, as an example my MCA carbine in 243 Winchester has a code of 63, meaning it was manufactured in 1963. The Mannlicher Schoenauer was a very expensive rifle to manufacture do to the large number of machining operations required, so to try and entice more Americans to pay the higher price that the rifle commanded, the rifle under went some changes. A Monticarlo style stock was fitted to make a sight picture with a scope, hence MC. That presented a problem using iron sights, so they lowered the comb, hence the MCA. The bolt handle was swept back and small changes to the magazine. The early Mannlicher models were referred to by the year they were introduced, as an example I have a 1910 it was manufactured in1914. The 1924 was called Sequoia and is fairly rare. You have 2 desirable rifles in a very good caliber. Here is a photo.
Mike