Slant 6 to smallblock

Having done this myself, I used the Schumacher Creative services kit. You will have to address the following;

Larger radiator and shroud
Small block trans
(If you change from a 904 to a 727, or the other way around, a driveshaft will ether be needed or cut down, stick with the same model trans for the swap.)
IF you have the 7-1/4 size rear, Inseriously suggest at least a swap to a 8-1/4, 8-3/4 is better for high HP/TQ cars. North of 450 HP.
Suspension wise, you will like it when you upgrade the T bars and springs but it is not an need now thing. It can wait.
Anti roll/sway bars are also nice & also fall in "Not needed now" but for surely they will be nice.

On my /6 - V8 swap, I did not add anything except new rear springs from springs and things (AKA ESPO.com)
1 inch over bend springs added a really nice rake to the car.

Small parts are always needed and there is nothing really to worry about. Extra wire and terminals help with what you have all ready.

It was generally speaking, pretty easy to do and it went very quickly. For exhaust, Inwent with regular Hooker Comps and a Jegs exhaust at 2-1/2.
For the rear I did a 3.21 geared 8-1/4. Very inexpensive and it can take some decent power for sure.
The trans was a 904 like the /6 had so the drive shaft bolted right in.