I doubt the 904 kit would effect longevity, it isn't radical compression and really isn't much bigger displacement than later model BAs or SMs. I used to bore out the old bikes about 20 to 30 over all the time and run Wiseco forged racing pistons with 10.5:1 compression. It never effected engine life. I would run a few top ends to 1 bottom end on those every time.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!