The only difference is the machining for the 4 x middle mains caps that have the extra bolts, and it is application specific. In passenger vehicle use (incl El Camino), 250hp (L65) and 255hp (LM1) were 2 bolt and 300hp (L48) were 4 bolt. That is about the limit of Tonawanda 1969 4" bore engine use in passenger vehicles, there may have been some 210hp (Camaro) and 235hp (Chevrolet) 327's but these were both 2 bolt anyway. Not sure what Trucks/Vans used Tonawanda engines but these are normally 4-bolt anyway. As far as I am aware the 388's were Tonawanda exclusive castings.

Here's a couple of 2-bolts, will both be an L65 most likely cast in 1969 (LM1 were 1968 only):
https://www.ebay.com/itm/Chevy-Small-Block-350-camaro-chevelle-3932388-C-6-9/264289978805?hash=item3d88e909b5:g:cfYAAOSwUv5bWz0Y

https://www.ebay.com/itm/1969-Chevrolet-350-Engine-Block-Casting-3932388-Date-D-17-9-Standard-Bore/133030336763?epid=656672483&hash=item1ef939d8fb:g:rkMAAOSwuTRcvkIm

Edited by user Monday, 27 May 2019 7:16:20 PM(UTC)  | Reason: Not specified

They should all be 1969 cast from mmeory. The only difference between manual and auto HT 350 engines (apart from the 2 vs 4 bolt) was the cc of the combustion chambers. The rest is the same. In the USA the LM1 and L48 had different distributor timing as LM1 was meant for regular fuel and L48 for high octane fuel. But here they were both for Super fuel hence the extra timing in the auto and a bit less in the manual (compared to USA). They had different build numbers on the carbs, but that is just the vacuum advance source (ported for manual and full for auto). In the USA you will pick the LM1 and L48 apart by the engine plant suffix code, but doesn't apply here, only the 350A and 350M identifiers. You won't find a LM1 in the USA with a 1969 date code on it though, but it is swings and roundabouts anyway as the only difference between an LM1 and L65 is the intake and carby so once it is a long engine they are the same thing. The engines we got here as 350A engines would have been built alongside L65's for US use, and they only became different once the HT sump, LH exhaust manifold and the 4BBL manifold went on, then of course got painted X2 engine red rather than Chevy orange.

Edited by user Monday, 27 May 2019 9:19:59 PM(UTC)  | Reason: Not specified

HT with 350 didn't exist until mid 1969. Remember the first one (1-A) from Elizabeth got a 327. So the chances of getting a 1968 cast one in a HT are rare. 1969 model year in the USA ran from 9/68 to 12/69 (it ran longer due to strikes). At the time the engine plants had their own block and head casting numbers, Flint (using Central casting blocks) used 386 later replaced by 618. Tonawanda used 388. They all changed to 010 mid 1969. McKinnon cast some 386 blocks too (we got them in the final HK GTS327's). You also find some example of Tonawanda blocks (and heads) being machined and assembled at Flint, and vice versa (probably strike related again). 386's were used in everything from 210hp 327 through to the highest output 350 in 1969. It is rare to find higher output than the 300hp L48 with a 388 block as Tonawanda didn't do big valve Fuelie heads, only the standard 1.94/1.5. There are some reports of Z28 302 engines using Tonawanda blocks but these are all Flint machined and assembled I think. In the end they are all interchangeable.

From memory 388's didn't exist past mid 1969, the 010 replaced it. This is why the last of the HG 330M engines have 010 blocks.

It is all academic anyway, as finding engines from Holdens over here is near impossible with so few made, and unless you can find the original from your car it isn't really worth the hassle as any engine is as wrong as another! 388 blocks in the USA and Canada will be as common as 253's and 202's were over here. They are always all over Ebay. If you want the right cast number just grab one from the USA regardless of the cast date, fluking the right cast date is like a needle in a haystack. But it will still have a US partial VIN and assembly code incorrect for a HT.