I have not done this exact swap but I have done swaps to 55.1-59. I am responding with just minor advise. I don't know what your experience is. I don't see it hitting in the pic. You can have the pulley as close as 3/8. I don't know if you have the motor at 4 deg down angle which you get when you level the carb/intake, if it has a carb. Chevy motors have a built in crankshaft angle to facilitate the pinion angle.
If the V belt has a smaller pulley that may help. Don't know if harmonic balancer would still be close. If the fan hits then a short would help, otherwise it's just for rad clearance.
There are smaller diameter HEI dizzys.
You didn't quantify the interference. Can't motor go upwards/forwards/tilted? I'm sure the AD boys will have the good info.
You said one thing at a time so I won't go further about any other issues for now, but they've been solved here before. No sweat.

Cutting/notching cross members is a no no IMO. Are you going to use a universal tubular cross members? That's what I use.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn