Greetings . . .
Based on the original the post it sounds as if you have yet to acquire an engine – and that some 302 engines/parts may soon be available in your area. Seems you are still weighing options before purchase . . .
The old Patrick’s site/catalog had a very succinct write up on stock GMC heads:
-----------------------------------------------------------------------------------
2136477
Open (Hemi) chamber, small ports (1 7/16"). Served as the only head, apparently, for '228, '236, '248, '256 & '270 from 1939 thru approximately 1954, with the sole exception of some '270's which got the new bigport "H" head (below). Compression was established by size of lump on the piston.
2193417
The legendary "H" head - open chamber, with large 1 3/4" intake ports, introduced in 1950 and used only through '52 after which (819) was used. Great for performance! Forged, custom piston shown.
2193983
'302 head - big ports, "D" chamber, always with a 2-barrel carb, it seems. Installed in larger GVW trucks (never pick-ups) from '52 thru '59. An accompanying governor limited rpm's to 3,200. Also, a great performer, with "D" chamber. Custom piston pictured.
2194819
Small ports and small chamber. This head was apparently introduced about 1954 to allow lighter, flt-top (or even dished!) pistons on '248 and '270 engines. '236 and '256 engines were already gone and now '228 and '248 were dropped, leaving the '270 to serve in everything down to 1/2 ton. These (6) engines are the "small-block" Jimmy family; sharing rod and main bearing sizes, connecting rods and head-bolt pattern.
Theoretically, any of the above heads could be installed on any of the blocks. However, the '477 head would be limited in performance by the small ports, and pistons would require some sort of lump (or, "pop-up) to make adequate compression. The '417 and '983 heads make excellent performance application with their large ports and good chamber design, though they are best installed on their respective blocks: '417 on a '270 and '983 on a '302 due to piston confiuration. By noting the photo, it is apparent that the '302 head would interfere with the '270 piston, and the "H" head would make less compression with the '302 piston. The 2194819 head is a poor performance candidate by virtue of its small ports and restricted chamber. (note that parts number reveals introductorysequence ) None of the stock GMC pistons is recommended for a performance engine, due to their excessive weight.
-----------------------------------------------------------------------------------
Eddie Edmunds cast that manifold for the then common 477 head.
Fast forward to today and you’ve got an uncommon Edmunds manifold in hand. And ebay has a NOS small port head available:
NOS GMC 2136477 Head 
regards,
stock49
