I think one of the least-expensive elements of a solution for you is evident in one of the pics in the Lotus thread -- the driver still looks like a tight fit but the steering wheel is tiny. If the steering wheel in that Lotus was the size of the SWB's, he couldn't even get in that car. The steering wheel on a SWB is probably close to 18 inches while that Lotus wheel is probably about 11 or 12. Though I'd much rather have an original steering wheel, a 14 to 15 inch aftermarket wheel looks okay in a Cruiser and buys you precious space.
In the SWB's original form, you won't be able to shift gears. Your left knee will be up beside the steering wheel and there is no way you'll even be able to close the door. It will be impossible for you to put your foot up onto the clutch pedal because your knee will hit the bottom of the steering wheel first, and the driver's door itself will get in the way.
I think an SWB is the smallest model of the old LandCruisers so you have the least to work with, though all old Cruisers are relatively small. Mine is not an SWB, but I was able to move the seat rails back a little, replace the column with the power steering conversion to a tilt and go with a smaller diameter wheel while gaining a little more leg space by increasing the column-to-floor angle. I still have space issues with both legs, including the shifter against my right leg in first gear, but I can now drive it somewhat comfortably and drive it safely.
For my next project, I'll get a longer replacement column which will allow an even greater angle and more room between the top of the clutch pedal and the bottom of the steering wheel. You'd think a longer column would work against you (everything works against you when looking for space in a Cruiser), but I needed more room for my legs under and around the steering wheel and with a tilt column you can negate some of the room you lose by using a longer column. The smaller steering wheel will also get some of this space back.
Hopefully some of these tricks will help you. I think you will need to combine some of these ideas with work to push the lower firewall/floor and pedals further out for an SWB. The headroom is less of an issue but you'll still stoop forward, but you're used to doing that all the time anyway, or your head has lots of dents in it.
I would worry less about modifying a 63 SWB. With your truck, you might even increase it's value by altering it so that more people could drive it comfortably. For "insurance," you can hold on to the original parts and if it turns out to be worth a mint someday, that in itself will make it cost-effective for someone else to return it to original.
Good luck!