How did the Super Beetle Conversion plate work? you might ask.
I bought an unfinished kit which came with a rolling Super Beetle pan and the SB conversion kit. There were two versions of the Super Beetle; one with MacPherson strut front end and the other with a beam front end. The roller had a beam front so I later sold the Super Beetle conversion kit to someone else.
As Wolfgang mentioned, the conversion plate bolted to the forward corners of the pan right at the forward bulkhead (firewall in front engined cars) - That would be the forward corners of the cockpit...There are two bolts on each side about 2" apart.
Then, it picked up the lower mount positions of the MacPherson lower suspension A-arms, as well as a couple of places in the central tunnel to anchor the front of the plate and position the beam mounts. Because the plate used existing VW mounting points, the only place where the spacing might be screwed up was between those forward mounting points and the beam mounts (the rectangular tubes sticking straight up with half-moon pieces cut into them). You can see those forward mounting holes in the plate in Wolfie's first photo.
Anyway, there isn't a lot of area there to move the beam mounts back 1", plus if you simply measured a pan car from the center of those four bolts at the cockpit corner to the rear of the beam mounts you would know where to place them if you were building a conversion plate from scratch.
I would be hesitant to try adding 1" spacers between the beam and the upright beam mounts because you're now adding a vertical torque arm at those mounting points that could fail over time. That wouldn't be pretty. It might be possible to create some new beam mounts just like those in there now but 1" thicker front-to-back and weld them right to the existing beam mounts to push the beam forward. Remember that doing so will move your steering column forward as well as your steering wheel 1" closer to the dash. Other things might be affected, I just can't think of them right now.
Will keeping your beam where it is right now affect handling? I doubt it. At least not that you'll ever notice. I was pretty OCD when I built my two kits and I'll have to go look at where my front wheels sit in the wheel wells and post a photo. LOTS of 356s have the front wheels a bit rearward in the wells. At least you'll fit in with the rest of us.