Repair re-re-pair

The Boo backed Yew primitive that I made about a year ago for my mate JT showed some nasty cracks in the grip area the other day so I've been working on a repair. There were cracks showing on the side of the grip, these had run down from the riser section which was a piece of small diameter Yew with the central pith showing and a few radial cracks, one of which had opened up severely.

I sawed off the riser section and rasped it down to the belly which is spliced Yew billets. I didn't want to remove too much wood and risk loosing the alignment of the limbs or creating twist in the bow. I investigated the crack by carefully wedging it open, I flooded it with low viscosity superglue and clamped it up in the vice. A new slightly longer and thicker riser section of Walnut was glued on and blended in. I thought that this repair would do the job and after a couple of days to allow the glue to cure thoroughly I put it up on the tiller. Slowly working it back and exercising it, I got it to 28" and ... BANG...

The Walnut riser split! The good news is the the crack didn't run down into the belly, and as it was on the tiller it didn't get drawn further and smashed (this is because it's a controlled pull via 2:1 leverage which can be stopped virtually instantly), so I can try a second repair. It dawned on me a day later that I could check what draw weight it failed at, by looking at the peak hold needle on the scale... it failed at 83# .
I spent a good deal of time deciding on a more solid repair and wondering why the Walnut failed, I think it was just some poor quality Walnut. Speaking to my Brother who has worked with a fair bit of Walnut on shotguns, he reckons it's possibly not Walnut, maybe the table top from which it was made was just some random tropical hardwood which was stained up to look like walnut. The surface of the table was certainly darker than the inner wood.
The plan I came up with is to let in a strip of Bamboo edge on into the Yew core, like a reinforcing I beam, then top it off with a riser of Ash with gain edgewise. To give some idea of scale, the groove was milled out using a 4mm end mill,

I've go the bamboo glued in, and then cleaned off flush. The Ash has been glued on and it's ready for shaping and the testing. The last pic shows the Boo strip ready for gluing in, the Yew is protected with masking tape, The pic shows the profile gauge which allowed me to fit the bamboo to the curved slot... it's curved to avoid too much of an an abrupt discontinuity at each end.
Update:- The repair was successful and the bow has been shot a good deal since.