Need longer engine output shaft

[OldChipper]

My 97 wheeled string trimmer finally worn out the 6HP B&S engine. Everything else is still in good shape. I have a nearly new 6.5HP engine, that would fit. Only problem is ,the output shaft is over an inch to short!
I could easily make a shaft extension, (I'm a old retired experimental machinist) only thing I need to figure out is how to make sure the shaft is balanced close enough to not damage the engine with the extension added. It's not like there are blades on it, just a 4 inch drive pulley. Been trying to find if someone else, has tried this. (Don't want to reinvent the wheel if it's been tried before.) So far I haven't found anyone that has tried it. An old small engine repairman was pretty sure B&S use to make one some years ago. I could easily balance it, if I removed the crankshaft. I don't want to do that unless I have to.
Would welcome any ideas or comments anyone about this.

 

[mechanic mark]

Have you tried a 1" long bushing & a longer bolt to fit?

 

[shiftsuper175607]

My 97 wheeled string trimmer finally worn out the 6HP B&S engine. Everything else is still in good shape. I have a nearly new 6.5HP engine, that would fit. Only problem is ,the output shaft is over an inch to short!
I could easily make a shaft extension, (I'm a old retired experimental machinist) only thing I need to figure out is how to make sure the shaft is balanced close enough to not damage the engine with the extension added. It's not like there are blades on it, just a 4 inch drive pulley. Been trying to find if someone else, has tried this. (Don't want to reinvent the wheel if it's been tried before.) So far I haven't found anyone that has tried it. An old small engine repairman was pretty sure B&S use to make one some years ago. I could easily balance it, if I removed the crankshaft. I don't want to do that unless I have to.
Would welcome any ideas or comments anyone about this.

They sell longer output shafts, bought one in the distant past...don't remember where.