First, do you know about this web group of Bristol boat owners? It's pretty active and a great resource.
bristolboatowners : Bristol Boat Owners
(that's my boat on the welcome page)
Check it out.
About you're measurements........
As they say, a picture is worth ..... well, a lot.
Width of well, 10 inches
Depth of well, 16 inches
From the top of the motor mount/inside transom to the bottom of the lazarette lid
18 3/4 inches
but, my motor mount / inside transom may not be as "tall" as yours. I've noticed that my motor sits down pretty low in the water. Two advantages, the prop is less likely to come out of the water in choppy seas and there is lot's of clearance for a larger motor like mine. so, here is a picture of the "height" of the motor mount transom
Hope all this answers your questions.
Prince William Sound