on existing unit- in back, there are the 2 holes but neither is up under the trim tab-the hole youre talking,on MINE,actually"splits" between the body and the cavity edge under the tab plate.On the new unit,all the HOLES line up with existing unit's(existing one is still on boat-am measuring)but the bolt hole is up in the tab cavity like you mention-so basically the trim tab cavity "starts sooner" on my new unit-1/2 in maybe but im pretty sure its al gonna line up ok cuz theres a slight angle difference between the two at the final angle/end point that will make all seams come together ok,etc...Ive done a little homework the last day or so talkin to a few local guys and am gonna have a guy look over Monday-compare,maybe put on the new (used) unit.Right now i have very slightly bent prop shaft and completely worn off skeg!!(not done by me-just bought boat).Hopefully i get a nice fix here.Unit only costs $100.00-will probably put in new impeller.I hear that is good procedure while you have a unit off /out of motor,yes???