Beck has always impressed me with the amount of floor space available due to their tube frame (even the center tunnel is lower/less intrusive). A VW pan limits both foot and seat space. A pan-based car limits you to an 18" (to maybe 20") wide seat due to tunnel and side sills. However using an ancient VW pan often makes it easier to register often as the year of its VW pan - which can exempt smog testing requirements and allow for antique plates.
Check out Troy's website to see the various VS body styles from the classic to ultra-wide body cars.
Speedsters |https://speedsters.troysloan.com/
Rear vs mid-engine? For about 11 years I drove a Porsche 914 which was mid-engine. I did normal mods to it - anti-sway bars (F&R), Koni struts, alloy wheels with Michelin XAS radials. It handled predictably at any speed - no tail-wagging engine pendulum.