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You should be fine with your guidescope as its a 4 inch refractor and not that demanding of guiding. Flexure is more of an issue in longer focal lengths generally speaking.
The Lodestar would be way better than the noisy 237 chip. I think also quite a bit wider FOV and you would almost always have a choice of guide stars.
I recently mounted an SBIG STi guide camera with the SBIG lens guiding kit which is all nicely made with very solid rings like that on my CDK17 at nearly 3 metres focal length. I was getting round stars at 15minutes in some orientations but flexure in other angles. I have since rebalanced my rig and perhaps it would work better now.
So the point being that sort of setup should work fine as long as your focuser for the ST8 is rigid. That may be the weak link.
Roland Christen recommends the guide scope being attached to the OTA tube not other attachments. But most likely you will get away with it here. But if you do get flexure that and the focuser would be the first 2 things to check.
Greg.
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