Bolted the rebuilt 425 to the turbo 400 and set it in the frame of my 53 Olds today (the front end has been replaced with a 1974 Nova front end for steering/disc brakes). The good news is that it looks like no mods needed to the X-frame.But...the fit will be tight .Compared to my 53 parts car, the 425 is 2 inches longer from the back of the heads to the front of the fan,and there is only about 2 inches on the 53 between the heads and the firewall. Because of the design of the cowl in front of the radiator I would like to use the stock radiator location if possible.Thinking that probably should set the body on the frame to make sure the motor is in the right spot .Also ,the motor mounts hit only air .Looks like a universal cross mount will not work with the rear steer so thinking about using a plate back from the center support. Any ideas? A couple other questions. Is a water pump with a shorter shaft available ? Also,I can't find the thread, but I remember reading about a water pump with the outlet on the driver side (which is where the radiator outlet is on the 53 ).Finally, looks like the alternator bracket may not clear the inner fender well -seems like I also remember reading about a way to move the alternator to the passenger side .Would appreciate any assistance you can provide, THANKS.

 

 

That seems like it sits WAY back, but I don't know those bodys all that well.
When you said nova sub frame I figured it would be an easy fix, but as I look at what you are working with you have some custom fab work to do.
As far as the WP goes you can use a 1964 330 non air water pump. THat is the one with the drivers side exit. But you will have to find an early power steering pump and brackets because the newer style won't fit with that pump.
Then you will have to find the matching passenger side alternator brackets. I don't know if the 65^ non A/C alt bracket will line up with the old water pump.
You have some trial and modification in front of you.

 

Your facing the same problem I faced installing the 455 in my 57 Olds. I used the front two hole on the block for the engine mount and build mounts that I bolted to the front cross member worked out well and were simple to fab.

For the radiator I had a shop relocate the lower inlet to the right side. Easier to find the standard water pump then the more rare left side water piump.

I used the alternator bracket off of a 64 or 65 cutless without ac it bolts to the right side and works out well for the alternator

I had to enlarge the hole in the X member for the long shaft turbo 400 I converted to a single drive line so I could be sure that it could handle the torque.

There are more details and linked pictures to this thread detailing the motor mounts https://classicoldsmobile.com/forums...gine-swap.html

 

Your Nova subframe is the same as the one used in the 73-74 Omega. The 350 Olds in that installation uses the front two motor mount bolt holes, as Citcapp suggests. You need the Omega 350 Olds frame mounts, which will let you bolt the 455 directly to the stock mounts.