NOTCHED TRANSOM?

tx guys, the 150 is a 79 model. the 175 (25") is a 92. have to remove powerhead on 79 if i want to change mid section. never heard of spacer b4. just wanna run 150 till i get 175 runnin. i picked up a ss gill bracket and swim platforms today for 50 bucks. came off of an 05 kencraft center console that got TRASHED in katrina. i had to pull it myself but, still sounded like a good deal. only took 15 min. i dont know. i prob paid to much. anyways thinkin i will mount bracket 5 inches lower and run 150. just fill holes with 5200 later. or is that another bad idea? tx guys