Re: 350 to 454 swp
Just did this on my '73 3/4-ton Suburban. Radiator top mount part number is GM #6262164. Only $15 from Chevy.
For the engine mounts, I used the stock small-block mounts with the Energy Suspension inserts, like Shawn did. I tried to use the big-block mounts, but the mounting hole pattern is different and wouldn't work.
If you are interested in other details about the swap, just let me know. I have all part numbers and prices, and everything is pretty fresh in my mind, since this was done very recently.