also it helps to use the cowl and the back piece of the origional subframe to set some factory dimensions on the width. When my dad and i changed out the subframe on my 29 phaeton we ye tackwelded in spots for the crossmembers and then used self tapping sheetmetal screws to secure everything to make sure everything lined up right. We used a complete subframe from a 2 door so i am guessing that you will be fealing our pain pretty soon. Don't be surprised when you realise they are different from old henrys.
tk