How To Mount Small Outboard On The Grand Banks Wooden Dory

I have a 18' dory and a 5hp Mercury long shaft. I would like to power my boat with this engine, but the transom is to narrow (tombstown stile) 19">3" on the bottom.
Does anybody have an idea how to help me out with my problem?
(I would like to avoid cutting the hole on the bottom for the engine well)

 

i spose the transom is steeply raked
You could take 4 lengths of alloy tube, 1.8 wall, cut them short at top and longer for bottom two, to give you 13 degrees rake, draw it on floor, then put large flat washer against the transom and the tube , thru bolt with c/s, or if room hexheads

 

Thank you for responding to my qwestion Lazeyjack !
she is a tradytional banker dory with 14' bottom and 18' steam to stern, so
you are right about the rake!
Useing the tub is a good idea but in stead of washers and bolts, I will weld
them to sum sort of ss plate, to get more support for the transom.
Stearing with the tiller is anather problem, bicouse of transom top above engine, any idea?

 

your cav plate need be abt inline with run of the botton or 3/4 inch up, so work from there,