Yes, good spotting the M107 sidecover. Gearbox is wider ratio than pursang. They had fairly potent porting tho, but smaller transfers than Mk6 or later pursang.
While were on the subject are there any barrel/porting differences between mk5/6 and mk7/8,and what year did they go to left hand change? 
I'm fairly sure Mk5 pursang had smaller tranfers, not unlike the M107 SD matador, but diff part # to SD.
From Mk 6 (M103) cases were changed to incorprate much better transfer ports w 4 full transfers (in place of small & shallow secondary 'S' ports machined in the liner).
I'm also fairly sure Mk6,7 & 8 250 pursangs all used M103 (Mk6) barrell. Mk8 (M135) cases are a little bit diff in the transfer area to M120 (Mk7) & I presume Mk6, but not a lot.
They went to LH gear change in 75 model Mk8 (M135) - tho they actually came out in late 74
