Transdapt 4686 Swap Mount Motor Mount Chevrolet Small Block V8
http://bit.ly/1bhjdPWV8 Monza mounts require the frame adapter plates from a V8 Hbody and some mods to fit 2129's
Header tube sizes,there may be some others or exceptions:
Hooker 2129 -1 3/4" super comp V8 Vega conversion headers
Hooker 2135 -1 1/2" V8 Monza factory mounts also fits Vega
Hedman 1 5/8" V8 Vega conversion headers
Don Hardy 1 5/8" V8 Vega conversion headers
Sanderson 1 1/2" shorty Vega headers
Do you have the one or two piece rear main seal SHP version ?
V8 Vega oil pans are easier to come by for the two piece.
You will need to upgrade a few things for the V8:
radiator- (you will need a bigger one so look at Griffin aluminum units)
rear end- (swaping in a GM 8.5,Ford 8.8 or 9 inch will also allow larger brakes in the rear)
rear control arm mounting points- they are spot welded to the sheet metal floor (unibody)
rear control arms- the 40+ year old rubber bushings should be replaced or use aftermarket tubular control arms
brakes- (S10 spindle swap up front gives you 5 lug rotors and larger brakes)
front springs- (you may get by with stock springs if you relocate the battery to the trunk and use aluminum heads, short aluminum waterpump,aluminum intake and aluminum radiator)
Heater- if you are retaining the heater you need to flip the core to relocate the inlet and outlet tubes on non-AC cars