Well I did it. Over a two week period of time, I pulled the huge 235 and installed a much smaller 350 that makes 3 times as much power.
It wasn't easy. In case anyone is thinking about the swap, here's the issues and how I dealt with them:
1. The bellhousing is first. I had to find a bellhousing that matched both the SM420 tranny AND the 350. They were made by GM up to about 1990 I guess, and not too hard to find. But I had to cut out a space for the 350's starter to fit through and get to the flywheel. Angle grinder with a cutoff wheel will go through iron like butter.
2. The new bellhousing is the same size depth-wise, and mounts to the tranny crossmember if you drill two new holes.
3. The firewall will not quite clear the valve covers. Nor an HEI distributor. It will barely clear low rise valve covers and a conventional distributor. Anything else will require slight modifications to the firewall.
3. The steering box is totally in the way. It either has to be moved over or replaced. I'm gonna try shifting it over first, but eventually would prefer to replace it with a rack and pinion.
4. Speedway Motors sells a universal crossmember to mount the engine to. If you get this, CHECK IT FOR FIT FIRST. I found out the hard way that they welded the mounting tabs about a quarter inch too close together and had to make modifications.
Another point, do NOT weld the crossmember in. Bolt it in. You really need the flexibility when installing the engine with clutch into the transmission's input shaft. I needed to be able to rotate the crossmember to allow the engine to slide back.
5. I used an old Corvette 10.5" flywheel, which required a Corvette clutch. That's 153 tooth. I know that will work, but I'm not sure about a 168 tooth flywheel!
6. Even with a long water pump, I need about a 3" fan extension to get the fan close enough to the radiator.
7. The stock gas pedal can be modified to work with a cable. Unbolt the solid rod and use that to mount the cable too.
But that's it. Looks really good in there. There is so much room above the 350 that you could easily hide a big 8-71 and no one would have a clue. I've still got lots of nitnoid details to attend to, but the worst part's done.
