1- the truck manifolds are recommended for narrow bodies because they fit the cramped engine bay and are cheap and widely available.
2- the DS is
always going to be problematic because of the seemingly endless array of possible combinations: early, late, manual, column, 360, 318, [brand] heads. beyond
bone stock it is nearly application specific. but if you have the time, money and inclination to test fit a bunch of different manifolds, you could probably find something that works.
3- 340 manifolds are
NOT hard to find. i don't know why you keep insisting on pushing this fallacy. look, dan, right now, right here, on this forum's
very own classifieds there is a set:
[FOR SALE] - 68-70 A-Body 340 HP Exhaust Manifolds $550
4- what about [blank] manifolds? i suggest you go back and re-read section 2 from above.
5- yes, there was a police package 360. it did not have special manifolds. and if it did, it would be unlikely for the DS to fit because they came in 80's cars that have transverse t-bar suspension, isolated k-frame and column shift.
so, we are back to our usual starting points, which i will list for those of you still following along:
1- get a car first
2- worry about stuff later
3- you aren't going to make enough power for anything beyond dual exhaust to matter.