Running into a little issue here and need some expert help. The NCRS judging manual (and most other resources) have the 1970 LT-1 heads as casting # 3927186. I have also seen :

3991492 350 LT1, 70, 64cc, straight plug, camel hump. These were never listed from 1970-72, so what gives?

 

The 186s are correct for your 1970 LT-1. This particular casting was used in various application during the 1969 and 1970 model years. It was available in both small (1.94/1.50) and large (2.02/1.60) valve applications as well as pressed (small valve) and threaded (large valve) rocker studs. The heads that utilized the threaded studs also had stamped steel pushrod guide plates installed and were used in conjunction with hardened pushrods. Regardless of the application, accessory bolt holes are drilled and tapped in the end of the heads. Nominal chamber volume was 64cc although actual chamber volume usually falls closer to 66cc - 68cc. The intake port has a nominal volume of 160cc if I remember correctly.

I also see 3973414 as a possible casting for 1970 LT-1 applications. While this may be accurate, I can tell you that I have never actually seen one in person (and I've seen more than a few LT-1s).

The 492s are the replacement head for 64cc chamber, straight plug small block heads which require accessory bolt holes. They were never installed on any 1970 LT-1 as original equipment. I believe that this cylinder head casting is still serviced by GM, although it has been a few years since I actually checked.

Hope this helps you out.

Regards,

 

I believe that the 492 is a service replacement head that GM currently offers for the 70 LT1.