they are exactly like the 336's
No they're not. They are all derived from the same original designs from the late 1880s, but today, the bolt design is different on the rifle caliber guns, and this has been true for a very long time. Only the pistol caliber guns and the .22 rimfires retained the original late-19th-century design pretty closely.
1894:
336:
Different sized internals? Not true at all, except for a few that are obvious, due to different length and diameter of cases, etc.
A lot of parts fit all the Marlin centerfires.
The receivers of the 1894, 336 and 1895 are all different lengths, not thicknesses.
It was Winchester that used the 94 receiver for both handgun and rifle calibers. Marlin makes a true pistol caliber rifle, .30-30/.35 Rem rifle, and big bore rifle, all sized to fit the rounds they shoot. They make 4 different receivers, models 39, 1894, 336 and 1895. The 336 and 1895 are very similar in design, but different lengths.