The Synergy Reef 34 should fit. The 525 sump is 34.5" x 19" x 16" with a bit of extra wiggle room. The Synergy is 34" x 16" x 16" with a 10g fuge. Trigger Systems also makes a 34" x 15" x 15" with a 10g fuge.
The other option is to use the Red Sea sump with a couple pieces of glass cut and some silicone. The fuge section would be around 13g in this setup after removing the socks. Skimmer section might be a bit tight at 19" x 9" but there are a lot of skimmers that fit that profile. If you don't mind a larger change, you could cut out the first section and put in one more baffle to create a very large fuge area (17g-ish) and a 19" x 10" skimmer section.
Here is a simple mock up with before and after shots. First image is the unmodified sump. Second image is adding two pieces of glass no other changes. Third image is cutting out the first section and adding one baffle to divide the fuge and skimmer section. Total cost on any of these is going to be less than $50 and fairly minimal work.