Will this work?
 

I'm making asymmetrical blocks for a wall hanging size quilt. Each block has three borders, the first two cut on angles, the last one making the block an even rectangle. But because of all the variation, the blocks are coming out different sizes. I don't mind that, but I want them to line up for the finished quilt. I thought I'd take some strips of sashing fabric, sew a bunch of the blocks in a row, and then trim to a uniform size. I can sort of picture this in my mind, but will it work? Any thoughts? I can post pictures if that would be helpful. Thanks!!

Pictures are always great for seeing what someone else is talking about!
From your description I don't think of any reason why your solution would not be succesful.
Another similar method would be to draw out your desired finished size shape, make several copies, lay your current blocks on each and finish the final step as paper piecing. Disclaimer - I have not tried this either but it should work. Lol!

IF I understood what you are saying:

I think I would get all the blocks to be the same size before trying to put sashing BETWEEN them

To get them to be the same size, I think I might try one of the following:

1) add a fourth row to all (or some) of the blocks, then trim/square to a uniform size

2) trim all the blocks you have now and trim/square them to a uniform size

If you want the blocks to line up and not be a nightmare to work with, I don't see any way around some trimming of the units to a uniform size.

If you would like it, then that is what you should do. You are right they would have to end up all the same size. Can't see why it would not work.

I'm going to give it a shot!

I am working on something along the same lines. I am going to applique my blocks onto a solid piece instead of using sashing, that way my blocks don't all have to be the same size (which I didn't want)

I'd love to see a picture of what you're working on. I don't really applique, but maybe someday I will!