The 400 rear pto is 840 rpm at 3400 engine rpm. front and mid pto are 2000rpm.
you will also have to extend the steering arm between the front axle and steering actuator. also fabricate a longer pto control cable, head light wires, fit a pair of 430 side panels if you intend to run side panels. hood side decal will have to be custom made or spliced. and then there will be that pesky exhaust exit to take care of.
might also need an electric ''pusher fan'' at the grill to make sure all that engine heat will get to the other side of the front grill.
also I believe the 430 frame is an inch or so narrower. so even if you splice two 400 frames, you will have other fitment issues to solve where sheet metal and brackets meet the frame.
might be easier to fab a one piece ''flip front-end'' out of the 430 pieces. THAT, would be a new one. just an idea I had. I once built one for my 55 chevy back in 77.
I would first figure out if the 430 hood is wide enough where it sits over the 400 heat shield. might be tight there. these hoods taper in, in width wise as they approach the steering tower.
I would definitely put a 430 side by side with the 400 and take some serious measurements, and get it worked out on paper and in my head before I started spending money. I am sure there will be other issues, you cant plan for all of them. later, JZM