If the question is "Can you use electric TC3 parts on a TC4?", then the answer is yes. There are various replies/examples in the TC3 and TC4 thread here in the on-road forums on RCTECH.
If the question is "Can you use nitro TC3 parts on an electric TC3/TC4?", then the answer is also yes. The best example that I know of is an aftermarket chassis for the TC3 made by Xtreme Racing. Check out the following link to see an electric TC3 with Nitro TC3 suspension & steering. (http://www.xtremercracing.com/Produc...10040&pID=1155
Here is a picture of the bottom of the chassis (note the multiple holes for a-arm mounts):
The main challenge when swapping parts between the NTC3/TC3/TC4 involves modifying parts for the different diameters of the hinge pins.
Sometimes can enlarge a hole to accommodate a larger pin, but you will weaken the part.
You might also have to sand/file some parts to fit, which can also weaken parts.
If you were simply wanting to install something better to adjust rear toe, Associated makes 3.0, 2.5 and 2.0 degree rear blocks (in blue aluminum). 3-Racing also makes rear blocks in 3, 2, 1, and 0 degrees. Here is a link showing 3-Racing TC4 upgrades (http://www.3racing-parts.com/shop/te...1_596_666.html