Appreciate all the responses. I have certainly learned quite a bit. I originally intended to use what I had available (J-heads with gasket matched LD-340, and went with an XE262 from previous advise).

Pulled the motor this weekend and found it is a numbers matching 1975 318.

After reading all this information I have chosento keep the matching numbers block on the 1975 Hang 10 Dart and, if possible, still use J-heads/intake but realize I may have to return the cam and get a better one for the combination I chose to go with.

I have decided to rebuild the bottom end on a reasonable budget. Some options are:

1) get higher compression pistons and use existing reciprocating components. I am guessing J-heads may not be the best choice and I can certainly change to some with 1.88 valves. Need advise on cam choice.
2) get a stroker kit for the 318 (any recommended kits or suppliers?) and keep the existing heads and intake. Need advise on cam choice.
3) open to other suggestions

thanks!