I might be wrong here but I think the wait times for a Marsha are a few months and modding a personal amp to Marsha specs is about a month/month and a half. It makes sense that modding an amp would be a shorter time than building a Marsha from the ground up but I'm not sure how Dave has his requests set up, etc.
I know Dave is pretty busy right now because a flood of orders have come in recently. My amp is being modded and he told me it is anywhere from 4-6 weeks but that depends on alot of different factors.