Hi FireTech, thanks for posting the pics up. thats the first time I personally have seen the balancer. I suppose the sump is perfectly flat then? most only mention lumpy tickover which is solved by raising the tickover a bit. Can't say I have heard anyone complain about vibes much whilst driving, noise yes but not vibes. This is probably more dependent on which engine mounts and the tranny mounts. Saying that I'm sure someone will jump in now and say there vibrates like a SOB. It does add alot to the height though, how much do yo think? can you fit it in? Also I think the 4BT gets lumpier and noisier the more power that is extrcted out of them so if you keep it near stock it might not be too bad. Hopefully someone who has put the 3K springs in will tell you if it adds any more vibes or not. Do you know how much weight it adds? Might be worth a bit to sell, just something to think about. My 4BT isn't installed yet been too busy with my 6BT install.
If the balancer complicates the install it might be best to remove it. You can smooth the idle vibrations considerably by setting the idle up 50 RPM higher. Once the 4BT comes off idle they seam to be real smooth to me.
I wouldn't think the 366 spring would effect the balancer, but I don't know. It would seam to me the downside to the balancer would be parasitic power loss and possible decreased mileage, possibly slower to accelerate under light load.