KWWMINER

Great job! I purchased the Hasegawa kit for my Attic conversion and was in the process of fitting a resin wheel ell to the lower fuselage half and was also trying to fit a resin engine as well. The Attic fuselage ends and side seams on my conversion were atrocious beyond belief!  I cut off the front to the first panel line and did the same to the donor kit. Looked. Like this wa s going to work, so I did the same to both speed brakes. The resin wheel set fit well but was quarter inch short. I looked at a Wild Hare build and the resin wheel bay was a little short there too but only about 1/8 inch.
 
On to the fuselage side seams. These also bad as well. Ranging from 1/8 inch or less to almost 1/4 inch or more these were equally atrocious. The fuselage resin was flexing all over the place. The solution I came up with was To  put some blocks in the same position on the upper and lower fuselage halves and then countersinking a screw that would force hulls together as far as could go without distorting the fuselage. This would be done in six or eight locations. With fuselage stabilizes and the new donor kit parts installed, I would have a stable base where I could seal the openings from the back. Bondo for the front side and sand, sand, sand! The resin wings fit well, but the missile wells needed work.
 
I had resin Big Mouth intake and cockpit which would work. The cockpit tub would require some conversion work around the canopy hinges. This would have been a piece of cake, after all the other work. The instructions sagely advised that was a conversion for the advanced modeler. At this point I put everything back in large plastic box with a lid.
 
It looks like your approach was the more practical solution. Again, great job!