1969 Valiant Slicing

the proportions may look better if you threw a 2-3" roof chop into the mix.
i have some experience of shortening, i did a 1979 ford cortina (uk car). i took about 2 feet out the middle. the amount was decided by the seats, there's 2 crossmembers in the car floor at the front of the rear and front seats. i cut in front of both so the rear footwell and front seta mounting area was gone. it now had a bench 'front' seat that had to be notched in the centre to get 2nd and 4th gears on the floor shift. the rockers were rusty so i bought 1 repair panel that did both sides with a bit left over, lol. it was to be a summer car so the roof came off leaving the 'a' posts and screen and the doors were welded shut. welding the doors meant no sub structure was needed which simplified the job a bunch. and yes i agree with comments above it would look better with no roof.
good luck, i'll be watching from the uk.
neil.
ps my cortina took 3 evenings after work from firing up my petrol disc cutter to unmasking it painted, lol.