Having owned examples of both types , I can say there were some similarities between the two chassis , but there were more significant differences - most notably that the 113 was the last of the swing axle cars and the 'new generation' W114/W115 cars had the 'diagonal-pendelachse' or semi-trailing arm rear suspension which every Merc used until the modern multi-link rear suspension came in with the W201 series . The 113 chassis had a lot more in common with the 'Fintail' W110/111/112 series and 108 series which were contemporary to it .
The only engine which sort of crossed over between the 113 and 114 series was the 2.5L M180 derivative used briefly in the 250SL and , in a different form (with carburrettors or a different fuel injection system) in the 250 and 250CE models .
The four cylinder engines used in the W115 series were never used in any SL , nor was the M110 2.8L as used in the W114 280,280E,280C,280CE used in any W113 SL although it did make it into the R107 SL series . Some 114s did get the old single cam 2778cc motor but again with a different injection set up from the 113 280SL.