Lets build a CHEAP(!!!!!!!) bracket motor!

Assuming and hoping the mystery engine needs no machine work in the cylinders... and it is good to go....
Air cleaner $25 - ish
Summit Racing® Air Cleaners SUM-G30010B
Intake @ $220
Professional Products CrossWind Intake Manifolds 55026
Carb - 800 cfm remanufactured $464
Edelbrock Thunder Series AVS Remanufactured Carburetors 18139
Headers @ 180
1970 DODGE DART Summit Racing® Headers SUM-G9040
Exhaust pipe @ 15 X 2 = $30
Summit Racing® Exhaust Tubing SUM-640025-1
Muffler @ 33 x 2 = $66
Summit Racing® Turbo Mufflers SUM-631125
Exhaust clamps @ $4 each X 6 = $24
Summit Racing® Muffler Clamps SUM-G4625-1
Muffler hangers 2 x 7 = $14
Walker Exhaust Hangers 35210
Complete engine gasket kit/Magnum
https://www.summitracing.com/parts/slp-260-1723/make/dodge
Someone stated Oregon cam regrind @ $180
Unless you want a new cam... your looking at about double the cost, not included the the total tally below.
$1,203, oil, filter, gasket sealent and other sealent/chemicals not included.
Keeping the stock cam would bring you back to $1123. Now we’re down to $923.

Still not a bad quick shopping spree at Summit!
A classified hunt should result in good cost savings.
You could save a bunch with a FABO used AFB 600 carb instead of the Edelbrock reman @ there price. Even if you needed a gasket it and jetting kit you would be well ahead of the curve. You could save an easy $200.

I did drop the ball on a distributor. These can be found inexpensively. If you don’t mind taking them apart or learning them, a spring kit is a few dollars and this distributor is $41.
https://www.summitracing.com/search/make/dodge/engine-size/5-9l-360/engine-family/mopar-small-block-la/department/ignitions-electrical/part-type/distributors/price-range/20-50?N=price-range:20-50&SortBy=BestKeywordMatch&SortOrder=Ascending
Spark plug wires @ $32
https://www.summitracing.com/parts/sum-867807/year/1970/make/dodge/model/dart

Going up $73 smackers... back to $996.

Then go back and search out @318willrun thread on his hyper tuned scorcher. Every thing is always in the tune, carb and distributor!

Keep hunting the classifieds for those great deals! Drop the price further!
Trade with a buddy. I did a CF clutch DF set up for a converter I needed to get something running now instead of later. Hell! Works for me!
(Makes me wonder about the final cost in adding a converter and gears.... and probably new sneakers after the upgrades, I’ll for surely need some sticky ones!)
All that plus the motor like I saw for 250, and away you go.
Do these just bolt up to a 904/727 transmission?