Found a good '03 GS500 motor, I have a '79 basket case GS425. Will the motor fit? Plug and play, or am I going to have more problems than I have now? The 500 motor comes with carbs, harness and cooler. I'm worried about the airbox and exhaust. Git 'er dun, or turn and run?
Thanks!
joe

I'm brand new to the group, so if this has been debated to death elsewhere, I apologize!

Yes.....I believe the engine will bolt straight in but...........the pipes wont!

On the GS500 the ports are more or less facing forward and the headers exit between the frame uprights. On the GS425 the ports are angled outwards to allow the headers to clear either side of the uprights.

You will find there is not enough clearance to accomodate the 500 pipes in the 425 frame 

Compare the pics

So it will look something like this if I get the motor installed?

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Well... You could modify the frame to fit the gs 500 exhaust, fab up your own exhaust, or just quit. Easier said than done though!

theoretically .. a gifted exhaust welder 'could' fabricate you a set of headers that either slant away to the sides at 30deg or so ... or .. put a tight enough mandrel bend in a set? ....like bent or slanted just about right off the hole  ..... how a slant or bend that close would affect the gas flow/heat situation?? .. 

ive seen some hectic tight pipework done on rally/drag/weekend warrior cars .. whatever works for them got done really...