The 318 and 360 are of the same engine family, but are not the same style of engine. The 318s are more of a "square" engine with bore and stroke similar. The 360 is a long stroke, big main bearing diameter engine. The long stroke increases low end torque more than the size in CID would indicate. A relatively stock 360 out of a truck will normally outpull a built 318 as most of the hotrod parts increase the upper end, and reduce the low end, in a 318.
I have seen relatively low rpm 360s put together that can top 400 ft-lb of torque, maybe 310hp, with a redline under 5K. Such an engine does need to be built be someone who knows what they are doing more than the local garage, but the parts are all readily available.
727 transmissions may all be the same design, but the guts are all different for the different applications. A 426 Hemi got a 727 and so did some very low hp engines, but they were not the same transmission. Truck ones are also different from car ones. 727s can be built to handle pretty much anything you could do to a 360, but a stock 318 727 would probably have an issue.
In that van, you should have a 4:10 rear end. If you have a lower numerical than that, you should change that out first thing.
