Hello Robert.

Since I am just finishing my own Model 19 clone I can offer a small bit of advice.

Consider building this of Baltic Birch plywood. Much more expensive than mdf; around $100/sheet vs. $35. And bracing the cabinets. The lower base stiffens the bottom and the upper cabinet stiffens the lower cabinet top. The backs, fronts, upper top and sides could use treatment. I used around 1/4 cubic foot of bracing made of 3/4" x 2" baltic birch. It does a fine job.

I would be surprised if anyone could build a pair in less than 50 hours not including finish.
At $40/hour, you have 2 grand in labor and maybe $500 in material. It took me longer and I used plastic laminate in stead of wood veneer. Speaker box construction comes with a learning curve that a regular custom furniture maker will need to include.

good luck with your project.

Les