Engine Performance problem
1985 Peugeot 205 4 cyl Front Wheel Drive Manual 50000 miles

Fuel pump is good, clutch is new, new spark plugs, new contact points,engine had just made an overhaul for overhead cylinder, gear is well condition, broken exhaust pipe at the middle of its all span. Engine starts high sound because of broken exhaust then when it takes the first gear change it accepts but no acceleration , it goes slowly if you get it second gear change it also refuses acceleration and goes to stop after a while or continues to move with more slower speed than which it was slowly on the first gear chang. Thank you for your interest.
What are the best engines that can fit replacement of Peugeot 104 model 1976 with no modifications in chassis. Thank you.