Difference between D3400 and D311 engine?

What was the difference between the D3400 and D311 engine that was offered in the D2's?

-Jeremy

D3400 - used in the J-series (early) D2s, 3 3/4" x 5" - 35hp-ish
D311 - used in the U-series (later) D2s, 4 x 5", higher hp maybe 40, completely different engine design, but does use the same pony motor, can be interchanged with D3400 with a bit of work (things like bellhousing etc. bolt up but it's not a plug-n-play). Both engines used in other applications as well as D2s

Thanks for the reply! Some much to learn about these machines.

Most obvious difference is the D3400 has both intake manifold and exhaust manifold on the right side of the engine where the D311 is a cross flow design with intake on the left and exhaust on the right.

Injectors are a standard (relatively) high pressure type (approx 1750 psi) on the 3400 vs the CAT capsule type that crack at around 500 psi which are used in the 311.