I have all original 1986 Silverado short bed 305 cid with 3 speed automatic transmission, it got 161k miles on it I had been think to swap that tired 305 for new crate 383HT or 502HT what do I need to make that swap completely, I want it be strong daily hauler and will it fit that original transmission which I had it rebuild few month ago..  

If you go with the 383 you can use all your 305 accesories. Pulleys,brackets,EX. manifolds,motor mounts,etc. The 383 has plenty of Torque and is made for pulling/hauling. 400ft.lbs tq. from 2500- 4000rpm. 435ft.lbs peak @4000rpm
The 502 will need all of the above at substantially more cost. 502 alone is @$1400 more without intake.
You didn't say if you were planning on a turnkey crate eng. that includes pulleys and brackets but cost WAY more and with the 383 swap will not be needed.
I would purchase a LongBlock HT383 wich includes the heads & oilpan,valvecovers,balancer & intake.
Add and 1- 5/8" headers, 2- 1/4" to 2-1/2" Dual Exhaust W/Crossover. Not sure where you live but you may need to keep your Catalytic Convertors for the smog police. High flow Cats are available cheap now. Holley or Edelbrock 600cfm Carb. or a good Quadrajet for better fuel economy.
Hope this helps,
SSedan64  

I dont recommend a 383 for towing unless it has a forged internal balanced crankshaft.Cast 400 crankshafts are known for wearing main bearings.Thats mostly why Chev quit makin em.To many issues came out of them in trucks in the 70's when they where used.Under heavy workloads the casting has to much flex in the main journals which caused premature bearing wear.U want a strong puller,forged crank sbc or BBC,either can do.But,befor u go there,u asked of the tranny.What is it.Mine was 700R4.same yr86'.It wont hold onto a big cuber for long,less of big mod's.U gotta bank the case pressure if wanting it to last.the added torq will chew it up in time.Ive got a 86'305 in my 87'with a 400TH.With a heavy load it has all it wants behind a stock 305.so befor gettin to wild beaf the trany.No big shiftkits,have a trany shop do it the right way.Im pretty sure youve got a 350TH.if it a 3speed auto bakin a305.ina 1/2 ton.Stock 350TH's dont like lots of torq.but will beef real nicely with good parts.400's will do 4 a while but give in after while.Dont forget a trany cooler.Good luck!