WICruiser, Just a suggestion, measure and mark the location of of your firewall in conjunction to your frame. Use a straight edge held vertically on your firewall and mark where it intersects with the frame on both right and left side. Use a know reference point on the frame, a front shock mount or radiator core support mount to take all your measurements from, some point that will not change.
If you can mock up the engine and trans prior to making any permanent mounting points you will be happier. Finding an interference point during muck up is easier to adjust the once you have everything bolted on welded in place (don't ask my why I know).
The NV3500 should be a good choice for your setup. The shifter location is just about right for a 49' and with the right cam and rear gears it will work great. Do Your Homework!
