Top spacers are for the most part not the best idea with IFS. You can use a small 1/8 or 1/4" thickness tops to correct for a trim issue. Why ? You're phisycally shifting down the mounting point at the top of your strut assembly virtually entending the lenght of your struts. That in essence is not bad as long as you're not over extending your CV's, tie rods, UCA's and/or UCA's doesn't bind/contact any other parts. People with the SST 3.5" lift are reporting contact with the UCA and the springs at full droop. from Readylift website they don't recommend installing the preload spacers if your ride height exceeds 22" from hub to fender because i'd think they're accounting for the top spacer to put your assembly 2" more at full droop plus in combination with the preload spacer the entire assembly witll over extend your CV's or who knows what else. Combine that with some of the forum recomendations you to run a lifting strut (5100's) on top of your RL top spacer and you're doing the same thing the preload spacer is doing to your factory struts when it comes to the overall provided lift.
Best way to know, put your front wheels in the air and check for clearance issues aorund all areas, CV's, UCA's, springs, note your CV angles..., do they look angled down excessively ? Do you have contact with anything at full droop ?
This is a picture i found while researching the new truck front suspension. Look at the gap between the factory UCA and springs at full droop. what do you think will happen when you relocate the top strut location down with a big top spacer ? chances of the uca hitting the springs are likely.
View attachment 71699
This is the entire article where the picture above was taken
Engineer Dan Edmunds takes a deep dive under the Ram 1500 to explain its trademark coil-spring rear suspension.
www.autoblog.com
This is a little video that explain the issues you might run with top spacers. Keep in mind the video talks about installing top spacers in a Tacoma, but the concept applies to most IFS vehicles that use A-arms
Somebody with the RL lift with and without the preload spacers should be able to clarify angles for everybody if they document what they have and post pics and measurements ? Best way for everybody to know if it'll work or not ?