So you have purchased Eckler Xmembers and are you OK with those now? And now you just want to know about exhaust clearance?
Usually a set of Ram Horns will do the trick. You do NOT want to locate the cross members until the motor and trans are in there, mocked up. Firewall clearance, steering clearance, tunnel clearance, fan clearance, pinion angle, exhaust...... are all copacetic.
Corvette Ram Horns are larger diameter passages.
There is chatter about removing the orig Xmember and making frame weak and possible cracks due to proximity to front leaf spring rear hanger. I don't think that is a worry and you are replacing it with a cross member. If you can clear it, leave it. Other suggestions have been to cut it off, leaving some stickout so as to weld a new cross piece designed to clear whatever it has to clear. Don't trap the oil pan or tranny pan. You can decide about that during mockup. But maybe you are doing a IFS/clip and haven't said.
Lots and lots of posts on V8 swaps here. Filter it all and do what makes sense to you.
