migration of dyes and DNA thru alkaline agarose gels

Dear Experts,

I need to run an alkaline agarose gel to crudely measure the length
of a primer extension reaction (prior to doing a urea gel to closely
and accurately measure length). Does anyone know what the migration
of bromophenol blue and xylene cyanol are in alkaline agarose gels
relative to DNA size (or alkaline polyacrylamide gels)?

Thanks,
Sharon