In my opinion you are wrong in such assumption. if you get a chance to get hold of 2 Japanese vehicles of same make & model but 1 RHD other LHD open up the hood and inspect closely. chassis ( frame ) is common, punch holes for bolts are same on both sides. Firewall bulges are identical it is matter of which side which plant it is assembled at.
Vigo double cab, Hilux double cab, Fortuner, Prado 5 door are all on common chassis design and left hand to right hand conversion is matter of parts availability PLUS - the cabin can be pulled out for swap between chassis
check physical specs for above and you will have a smile.
locate the members in list - SHARABHI --- & --- CrashD send them a PM or email, they will reply both are BUSY dudes but always reply to PW members promptly.