Hard starting assistance please.

Chall,
Veeeeeeeeeeery good move getting the HEI dist. As well as eliminating the coil, p/up, cap, rotor, vac adv, etc, all in one sweep as problem areas, you get a hotter spark out of the deal.

Couple of comments.

[1] Did I read choke was connected to the coil? That might be pulling down the available voltage to the coil during cranking. These old cars often have additional electrical accessories [ eg, sound system ] added over the years with no thought about WHERE to tap into the reqd 12v; connecting these devices to the wrong area in the electrical system can reduce ign voltage & cause strange problems like you are having.
[2] When you install your HEI. Do not hook up the tach. Run a jumper from the bat [+] terminal to the 'Bat' terminal of the HEI to get the engine running. Once running, hook up the tach; then, hook up to original ign source. Purpose of this sequence of events to eliminate other possible trouble sources.
[3] Roughen the feet of the dist clamp with a file or similar. This is for good electrical contact to the dist. The ground return for HEI is through the dist body - clamp - block [ ground ].