I have the reversing transmission in my boat.
I believe all original vegas came with the forward only with the feathering prop to go in reverse.
I have a big bolt for filling the transmission, and also a smaller (maybe 3/8 knurled screw head) screw in dipstick. The dipstick is metal colored while the head appears to be bronze or brass. The dipstick on my MD6A is about 1/8 in diameter.
If it appears that your dipstick has broken off, maybe it's not inside the transmission? Maybe the previous owner (PO) broke it off outside the engine?
gh