You'll have plenty of room, and you'll enjoy that combination.

As a matter of fact, you may be lucky enough that the C4 mount will fit inline with your existing transmission cross member. That also will dictate where your engine sits reletive to the fire wall and radiator.

I have a 390 in my 51 F1 with a C6 and THAT is a whole different ball of wax space wise - clearances measured in FRACTIONS of inches.

 

Yes, I've seen crossmember modified to fit a C4, only involves some grinding and welding but the down side is if you have to service your tranny, the original crossmember is connected with rivets. There are after market crossmembers to replace the original and they bolt on so you can remove the tranny without pulling the engine too.I fabbed my own crossmember, works fine. The only problem is you need the mount for the tranny to be lower than the frame so as to get the correct angle. The angle of the tail shaft of the tranny needs to match the pinion angle of the rear end by 2 to 3 degrees or you'll have vibration issues.I'll try to post a pic of my 289 in my F1. Hope this helps.

 

When you wish upon a shooting star, all your dreams will come true.
Unless the shooting star is really a meteor about to destroy the earth.
Then, you're pretty much dead no matter what you wish for. Unless it's death by meteor."