Please help

On a 1986 Chevy 454, the distributor has two timing tabs: one for the standard timing mark and one for factory advance timing. The correct one to use is usually the tab that lines up with the “0°” mark on the harmonic balancer for initial timing.

Here’s a simple way to install it:

Rotate the engine so cylinder #1 is at top dead center (TDC) on the compression stroke.

Align the rotor to point roughly toward the #1 spark plug wire on the cap.

Install the distributor so the gear meshes with the camshaft and the rotor points to #1.

Use the timing tab that matches the initial timing mark, then tighten the distributor.

Start the engine and check timing with a timing light, adjusting as needed.

 Tip: Take note of the rotor’s starting position before removing the old distributor  it helps a lot when reinstalling.

I’ll go ahead and assume you’re not motorhomeless…. Because Id feel bad for ya but hate when you’re **bleep**ting on the parking lot down the road from my house behind your broke down Moho. 

And a normal person wouldn’t “buy” a rag tag broke down motorhome with the engine partially disassembled when they know nothing about engines.  How’d you tow it “home?”

You need to find tdc on the engine and then install the distributor correctly on 1 or 6 if you’re using 1 for tdc. And then learn how to time it. 
Find some detailed instructions somewhere and good luck. 
And maybe disconnect your exhaust first so you don’t explode it when you get the timing or firing order wrong a few times.