452's flow well and have hardened seats but can be crack prone but if yours are fresh/checked out you are past that. As said you'll lose your good quench (I'm a firm believer in it) and lower the CR. Might see if you can locate another 915 as recently on here there was a single for sale and there were 2 more singles in the last ~ several months or so. EDIT they were cheap as singles tend to be