March-early April is our peak snowpack in the Cascades so I hope you expect that this will be a snow-climb. I've never personally been up Buckner but I have summited Eldorado around that time of year. Skis or snowshoes might be necessary for the approach and parts of the ridge. I would advise against forgoing an ice axe because you will encounter steep snow-slopes at some point near the end where trekking poles alone would be dangerous. Cornices will be building and you may also encounter 5th class sections, a bergschrund and possible gendarmes on the way.
I won't say it's impossible but for me it would be an unreasonable risk in March.
I found some links to parties who ascended via the SE ridge, yds 5.8, on Cascade Climbers, none of which took place before June nor did they come from Park Creek Pass:
http://cascadeclimbers.com/forum/ubbthreads.php?ubb=showflat&Number=1127978I don't have a clear understanding of your climbing history but I hope you understand that this is a serious and technical undertaking. At the very least it will be adventurous. I recommend finding some partners also interested in your route.