The 200r4 doesn't have the low first gear if that helps any. It has a .67 od ratio vs the 700r4s .70 overdrive. You would also need a uni-case 200r4 if you went that way. The gearvendors unit is only .78 overdrive but will make your 4.10s to be 3.20 gear while in od. Those taller tires will bring that number down even more to id say about a 3.08 or so.
Board member Lemield has an gearvendors unit with th350 that he uses. Might want to give him a pm or something and see how he likes it.
Here is a gearvendors link
http://www.gearvendors.com/cg2wd3s.html