The original engine and tranny combo is heavier than the LT1/4L60E combo so weight wise you'll have no problem.
Matter of fact, the old time way folks lowered their hotrod V8 powered AD's by removing springs, sometimes down to just 2 springs but I do not recommend following those past practices, LOL.
Your straight axle frontend will work fine with that combination as long as it's tight with no play.
A major unforseen problem you'll encounter is shoe horning that LT1 in with clearance around the stock steering gear box. Theres many interesting techniques builders have used over the decades to remedy that problem, you'll have lots of reading to do on that. Going with an aftermarket power steering setup that moves the steering gearbox up towards the front of the frame is probably the best solution but be prepared to part with some $$$'s.
Another situation that comes to mind is having to remove the rear frame cross member that the OEM bellhousing mounts bolt to. It'll be in the way of your auto tranny. Again there's a few interesting techniques used from running without one (not good) to cutting the OEM and welding bracing around the tranny (good) to making up a total custom cross member (good).
It's all doable and many do it, it'll just cost you alot more $$$'s than installing a fresh 235 or 261.
Good luck
Dave
