need advise in a 318

Yes on both. look for an A500 trans out of :
# 1989-2001 Dodge Ram pickup 150/1500 V6/V8(2WD)
# 1989-2003 Dodge Ram Van B150/B250 V6/V8
# 1989-2003 Dodge Dakota

1998 Dakota came with a 318/5-speed and a few other years. Either 318's would be fine, but the older one might have more meat in the bore. Hard to tell, but you can weigh them and take the heavier one. Go with 302 casting fast burn heads and clean up behind the valve seats. Should give stock pistons a little boost in compression. Run a conservative cam, not too big or youll kill your bottom end. Isky 268 is about max for a stock convertor, 5 speed cam go a little bigger.

PS. Not all 318's are closed chamber. The 318 302 head is closed as the actual chamber is smaller than the footprint of the piston, ie if you surfaced the head, the chamber would look like a heart, not a circle. all other 318 heads are open, circular chamber. There is a quench area away from the valves, but it still is technically an open chamber. The 273 "920" head was closed too but I think they were the only closed heads.