More is not always better.
These older motor have more vibration and the gearbox is not as nice as a Blaster.
As well, parts supply is not so good as a Blaster.
If you know what you are doing, you could have an awesome powerful quad with the 465.
If you are just learning, by the end of the first afternoon it could explode into a pile of parts you will never fix.
As for the extension, hard to tell from the picture but it solves the pipe issue and the wheelbase is reasonable.
Two issues: The quality of the welds and is everything straight?
If you don't know about leak tests and how to get jetting perfect, you'd be best to stick with a Blaster.
The Blaster motor has the potential to easily make a reliable 30-40hp with a great gearbox and ample parts supply.
All while being very frugal on your pocket.
Steve